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Effect of inoculum on the anaerobic digestion of food waste accounting for the concentration of trace elements
Abstract
The production of renewable energy in the form of methane from the anaerobic digestion (AD) of food waste (FW) varies depending on factors such as the quantity and quality of the inoculum. This research evaluated the influence of trace elements (Ca, K, Fe, Zn, Al, Mg, Co, Ni, and Mo) present in inoculum from different sources (wastewater treatment plants (WWTPs): 2 agro-industrial WWTPs and 1 municipal WWTP) on the AD of FW. This study found that the source of the inoculum determines the content of macronutrients and trace elements, which can alter the requirements of the AD process and therefore affect methane production. The inoculum obtained from municipal WWTPs contain potentially inhibitory concentrations of Zn and Al that negatively affect methane production (<70 mL CH 4 ÁgVS À1), the hydrol-ysis constant (<0.19 d À1), and the lag-phase (>7 days). It was also found that high concentrations of trace elements such as Ni (35.2 mg kg À1) and Mo (15.4 mg kg À1) in the inoculum increase methane production (140.7 mL CH 4 ÁgVS À1) and hydrolysis constant (>0.18d À1) in addition to presenting short lag-phase (<1 day) in the AD of food waste.
... TM addition is needed to achieve higher methane yields, especially in mono-digestion. Numerous studies have been conducted using various types of waste, with a predominant focus on food waste [21,[28][29][30][31][32][33][34][35][36], sewage sludge and, waste activated sludge [37][38][39][40][41], maize silage [15,[42][43][44], slurry [45], methanol [46], wheat stillage [26], and molasses stillage [47]. In addition, accelerating additives such as Ti-based compounds have been used because they can enhance AD performance. ...
... Most research has focused on substrate degradation and biogas production rather than inocula [66]. Parra-Orobio et al. [32] studied the effects of inocula (from a municipal and two agro-industrial wastewater treatment plants) on the AD of food waste and concluded that the TM concentration in the inoculum had an essential effect on the performance of the AD working in batch mode or at the early stages of semicontinuous digester operation. ...
... This should be considered because no additional Fe was added. Parra-Orobio et al. [32] recommended determining the nutrient content in the inoculum to evaluate the actual need for the use of external sources of nutrients. ...
Anaerobic digestion is a promising technology for producing methane-rich biogas. Various wastes, including waste activated sludge, food waste, farm waste, agricultural waste, and wastewater, have been used as substrates to generate biogas, which can be transformed into electrical or thermal energy. However, process instability and low methane yield restrict the widespread application of this process. Several strategies have been employed to increase methane yield and energy production, including adding trace elements, such as iron, cobalt, molybdenum, and nickel. Trace elements are part of the cofactors of enzymes involved in methane synthesis and microbial growth. This review aims to analyze the effects of trace elements on methane yield and propose concentrations at which methane production increases, as well as potential inhibitory effects. The addition of trace metals to the anaerobic digestion process has been found to have positive effects, such as enhanced methane yields and productivities, volatile fatty acid (VFA) removal, and chemical oxygen demand removal. An analysis of previously published data from other researchers was adjusted to a variant of the Haldane equation, suggesting that ranges of mg of trace metals per gram of substrate added promote an increase in methane production (0.56–1.67 mg/g VS for iron, 0.01–0.1 mg/g VS for cobalt, 0.03–0.5 mg Mo/g VS for molybdenum, and 0.04–0.5 mg Mo/g VS for nickel). Furthermore, the literature review revealed that the efficiency of the process decreases with increasing metal dose beyond the proposed range. The frequency of trace elements addition directly influences VFA removal. Some trace elements, such as nickel, generate VFAs of higher molecular weight, modifying the process performance. Notably, the process efficiency decreases with higher doses of trace elements, although this promotes the VFA removal.
... These results confirm that the APESA inoculum used in this study had sufficient quantities of vitamins and trace elements and therefore do not need supplementation. Parra-Orobio et al. (2018) have investigated the effect of trace elements supplementation on anaerobic digestion of food waste using three different inocula (granular sludge from UASB reactor treating sugar industry wastewater, granular sludge from UASB reactor treating slaughterhouse wastewater, and flocculent sludge from USAB treating municipal wastewater) [34]. Results in the above study showed that addition of trace elements did not have any significant difference in methane yields with inoculum sourced from USAB reactors treating sugar industry but improved methane production from the same reactor treating slaughter of cattle and pigs [34]. ...
... Parra-Orobio et al. (2018) have investigated the effect of trace elements supplementation on anaerobic digestion of food waste using three different inocula (granular sludge from UASB reactor treating sugar industry wastewater, granular sludge from UASB reactor treating slaughterhouse wastewater, and flocculent sludge from USAB treating municipal wastewater) [34]. Results in the above study showed that addition of trace elements did not have any significant difference in methane yields with inoculum sourced from USAB reactors treating sugar industry but improved methane production from the same reactor treating slaughter of cattle and pigs [34]. Nonetheless, in most cases, if no preliminary analysis is done, it is unclear whether BMP inoculum or substrates tested will have sufficient nutrients available and supplementation can be recommended at the start of the BMP assays [9]. ...
... Parra-Orobio et al. [33] studied the effect of three different inoculum sources on the methane yields of food wastes. Results showed that use of an inoculum from a sugar mill WWTP (Inoculum I) and inoculum obtained from a treatment plant that treats wastewater from cattle slaughter (Inoculum II) had similar methane yields of 144 and 149 NL CH 4 kg VS −1 whereas the inoculum from a municipal WWTP (Inoculum III) had the lowest methane yields 100 NL CH 4 kg VS −1 suggesting that the source of inoculum can affect the methane yields [34]. In a similar study, De Vrieze et al. [9] studied the effect of four different inocula collected from full-scale biogas plants and their influence on the methane yields of four substrates (molasses, bio-refinery waste, liquid manure, and high-rate activated sludge). ...
Anaerobic digestion for the valorization of organic wastes into biogas is gaining worldwide interest. Nonetheless, the sizing of the biogas plant units require knowledge of the quantity of feedstock, and their associated methane potentials, estimated widely by Biochemical Methane Potential (BMP) tests. Discrepancies exist among laboratories due to variability of protocols adopted and operational factors used. The aim of this study is to verify the influence of some operational factors (e.g., analysis frequency, trace elements and vitamins solution addition and flushing gas), feedstock conservation and the source of inoculum on BMP. Among the operational parameters tested on cellulose degradation, only the type of gas used for flushing headspace of BMP assays had shown a significant influence on methane yields from cellulose. Methane yields of 344 ± 6 NL CH4 kg⁻¹ VS and 321 ± 10 NL CH4 kg⁻¹ VS obtained from assays flushed with pure N2 and N2/CO2 (60/40 v/v). The origin of inoculum (fed in co-digestion) only significantly affected the methane yields for straw, 253 ± 3 and 333 ± 3 NL CH4 kg⁻¹ VS. Finally, freezing/thawing cycle effect depended of the substrate (tested on biowaste, manure, straw and WWTP sludge) with a possible effect of water content substrate.
... The values of methane production potential (M o ) of the first-order kinetic model from UBP and RBP were higher than the one obtained in the BMP laboratory test. Parra-Orobio et al. [39], reported that the k value in the range of 0.025-0.2d -1 for the substrate is rich in carbohydrate. ...
... In contrast, the fitting between laboratory data and modelling of UBP did not show a good fit. In general, when a coefficient of determination (R 2 ) is less than 0.9, the data do not give a good fit between laboratory and modelling results [39]. In contrast, the fitting on the laboratory data to modified Gompertz modelling is not fitted well (Table IV). ...
Bananas are tropical fruits mostly eaten in Malaysia. The banana peels are high in organic, and putrescible caused the odour and leachate problem where it has been a dump. In practice, banana peels considered as a waste product that has been combined with municipal solid waste and dumped into the landfills. However, banana peels are bountiful in organic matter and high with moisture content. Thus, it could be a convincing substrate for biogas production through anaerobic digestion so that the major concerns of environmental protection is achieved aside from producing energy in a sustainable way. Therefore, this study was initiated to estimate the ultimate methane yield from the unripe banana peel (UBP) and ripe banana peel (RBP). Besides that, the assessment on the kinetics of the methane production from UBP and RBP is conducted using Modified Gompertz and first-order kinetic modelling. In this study, the anaerobic digestibility of banana peels measured in a batch reactor for 25 days each fed by UBP and RBP. The batch reactors operated at an inoculum to substrate ratio (I/S) of 1.0 and at a mesophilic temperature (37°C). The ultimate methane yields from UBP and RBP digestion were 847.57mLCH4/gVS and 1405.31mLCH4/gVS, respectively. The higher bioavailability (in term of COD, and solid) in RBP resulted in the higher methane production rate. Two first-order and modified Gompertz kinetic models were compared for the prediction of organic degradation, and the results indicated that the first-order kinetic model of the RBP fitted the experiment best. It concluded that ripe banana peels are the most preferable feedstock for the anaerobic digestion.
... Kumar et al., [41], stated that the pH of inoculums utilised for anaerobic digestion of food waste was 7.5, and that the inoculum was acquired from a wastewater treatment plant. Parra-Orobio et al., [42] and Forster-Carneiro et al., [43] investigated anaerobic digestion of food waste using inoculum from a wastewater treatment plant. Inoculum pH was 7.8 and 7.9, according to Parra-Orobio et al., [42] and Forster-Carneiro et al., [43]. ...
... Parra-Orobio et al., [42] and Forster-Carneiro et al., [43] investigated anaerobic digestion of food waste using inoculum from a wastewater treatment plant. Inoculum pH was 7.8 and 7.9, according to Parra-Orobio et al., [42] and Forster-Carneiro et al., [43]. The pH level that is measured may vary. ...
Food waste was massively disposed at landfills daily, and this method is no longer effective in managing waste due to the limited space and environmental issues. An alternative solution was explored in managing the food waste, and anaerobic digestion serve as the best solution. Food waste was digested anaerobically in a lab-scale and pilot-scale anaerobic digester. The performance of a batch pilot-scale anaerobic digestion of food waste, on the other hand, is less documented. The goal of this research is to look into a batch pilot-scale anaerobic digester for food waste, with a focus on methane potential and kinetic studies. A single-stage anaerobic digestion of food waste was carried out with an inoculum to substrate ratio (I/S) of 2.0. A variety of tests were carried out to identify the properties of the food waste and the inoculum employed. Effluent was collected daily for the monitoring process. The pH and volatile fatty acid to total alkalinity ratio (VFA/TA) were monitored daily to ensure that the anaerobic digestion process remained stable. The VFA/TA ratio suggested that the anaerobic digestion process was stable throughout the anaerobic digestion process. The methane accumulation for 26 days monitoring is 463250 mL. The ultimate methane yield of 5103.6 mL CH 4 /gVS was observed. The maximum removal efficiency for TS, VS, and COD in this investigation was 85.32, 94.15, and 93.52 %, showing that food waste was efficiently decomposed for biomethane conversion. The Modified Gompertz (GM) and Logistic function models were used to conduct the kinetic analysis. The results reveal that the GM model provides a higher R ² value than the logistic function model, thus the GM model is more suited in explaining the performance of the anaerobic digestion process.
... The aforementioned explains the low production of methane, because these elements are important in multiple enzymatic reactions that are specifically performed during acetogenesis and acetoclastic methanogenesis [38,41]. For Fe, De Vrieze et al. [42] and Song et al. [43] noted that the supply of Fe is important in the AD of FW for maintaining stability and increasing the buffer capacity of the system. ...
... Although the models generally presented a good fit (R 2 > 0.9) and a reduced error (RMSE < 15) [1,11] (Table 1S) based on the standard deviation of the kinetic parameters under each evaluated scenario, the TF model had higher uncertainty for P max , which is maximised as the S/I ratio increases, especially with the S/I ratio of 4.0. This could be associated with the lack of buffer capacity in the system, due to accumulation of VFAs in the medium, since an excess of organic matter allows the generation of this type of carboxylic acids that can inhibit the methanogenic biomass present in the anaerobic digestion of food waste (Fig. 1S) [41]. ...
The potential for obtaining renewable energy from organic substrates such as food waste (FW) and biowaste has generated increasing interest in the anaerobic digestion process. Kinetic models are used to analyse the impact of different parameters on biological processes and thus, to optimize them to achieve and to increase the quality and quantity of biogas. This study presents an approximation of the pre-dimensioning of semi-continuous anaerobic reactors treating FW, based on: (i) biochemical methane potential (BMP) assays, in different conditions of substrate-inoculum ratio (S/I: 0.5 and 4.0 g volatile solid-VS substrate ·g VS inoculum −1) and nutrients (with macro-nutrients (N and P) and micronutrients, only micronutrients (Ni, Co, Mo and Fe) and without nutrients), and (ii) the kinetic performance through three kinetic models (transfer function-TF, logistic function-LF and modified Gompertz-MG), using P max (maximum methane production) and R max (maximum rate of methane production) as kinetic parameters related to the hydraulic retention time. The best S/I ratios were below 1.0 gVS substrate ·gVS inoculum −1 with nutrients. Although the three kinetic models obtained a good fit (R 2 > 0.9 and RMSE < 15), the TF model overestimated methane production, due to its high sensitivity for the kinetic parameters, which can lead to oversizing in reactor design.
... Fe, in particular, works as an electron donor, electron acceptor, binding element for sulfide precipitation, and a transport system of the methanogens during the reduction of CO 2 to CH 4. The addition of Fe to food waste AD treatment plant cultures has been shown to increase CH 4 production by up to 42% (Kong et al., 2018). Ca can promote bacterial granule formation and sedimentation, reduce the inhibitory effect of long-chain fatty acids, and improve biomass accumulation during AD (Kalemelawa et al., 2012;Parra-Orobio et al., 2018). K has also been shown to promote CH 4 production during AD by increasing the alkalinity of the culture and supporting microbial growth (Parra-Orobio et al., 2018). ...
... Ca can promote bacterial granule formation and sedimentation, reduce the inhibitory effect of long-chain fatty acids, and improve biomass accumulation during AD (Kalemelawa et al., 2012;Parra-Orobio et al., 2018). K has also been shown to promote CH 4 production during AD by increasing the alkalinity of the culture and supporting microbial growth (Parra-Orobio et al., 2018). While a variety of studies have tried to determine the effect of elements themselves, few studies have analysed the effect of minerals in biochar and none have determined the level of contribution each element has to enhance CH 4 production. ...
The effect of biochar addition on the microbial community and methane (CH4) production during anaerobic digestion was experimentally investigated, focusing on the role of minerals in biochar. The biochar was prepared from pine sawdust by pyrolysis at 650°C and 900°C, respectively, and a subsample was leached with citric acid. The cultures with the addition of biochar, leached biochar, Fe, and leached biochar combined with Fe, respectively, were placed in bench-scale bioreactors for anaerobic digestion. Daily biogas production was measured by volume displacement method and analysed for CH4 concentration, which allowed the cumulative CH4 yield (YM) and daily CH4 production rate (RM) to be determined. Culture samples were also taken daily for volatile fatty acids (VFAs) and microbial community analysis. Compared to the control without biochar addition, the addition of raw biochar significantly increased YM by 46.9% and RM by 43.0%, while leached biochar only increased the YM by 33.2% and RM by 18.2%, respectively. The Fe-containing minerals in biochar were found to enhance VFA degradation and increase population of Clostridia and Methanosaeta, improving the CH4 production.
... Calcium (Ca) concentration in FVW digestate was the highest value as compared to iron (Fe) and magnesium (Mg). Parra-Orobio et al. [48] also found the calcium (Ca) concentration is higher than both iron (Fe) and magnesium (Mg) for food waste digestate. Copper (Cu) was lesser in concentration as compared to Zinc (Zn). ...
The anaerobic digestion of fruit and vegetable waste (FVW) presents a promising approach for sustainable waste management and resource recovery. By characterizing its nutrient profile, this study explores the potential of FVW digestate as an organic fertilizer. FVW, comprising orange, Chinese cabbage, cucumber, and tomato, was processed into a slurry and mixed with anaerobic sludge as an inoculum in a pilot plant anaerobic digester. The digestion process, conducted in batch mode under ambient temperature, was monitored over 10 days, achieving a stable pH range of 6.5 to 7.5. Results showed that the FVW digestate contained significant concentrations of essential nutrients: nitrogen (5.4%), phosphorus (6470 mg/Kg), potassium (13700 mg/Kg), calcium (17400 mg/Kg), iron (11500 mg/Kg), magnesium (3840 mg/Kg), copper (88 mg/Kg), and zinc (574 mg/Kg). These findings indicate that FVW digestate is a viable source of organic fertilizer, offering a high nutrient content, particularly in potassium and calcium. However, nutrient concentrations varied from previous studies on food waste digestate, highlighting the influence of feedstock composition on anaerobic digestion outcomes. Future research should focus on assessing heavy metal content and exploring the effectiveness of FVW digestate in sustainable agricultural practices.
... A minimal presence of calcium in various food waste samples ranging from sample 2 (0.0977 %) to sample 5 (0.2487 %) was observed as evident in Fig. 8. Biofuel production would be more catalyzed by sample 5 since it comprises calcium-rich foods [59]. Parra-Orobio et al. [60] observed that calcium concentrations greater than 150 parts per million (ppm) in inoculum improved granulation processes and biogas accumulation. It is also observed that biohydrogen and biomethane gasses increased by 195% and 338 % respectively when 1 g/L and 3 g/L of calcium particles from calcium-rich egg shells were added to the bioreactor [61]. ...
... Wang et al. (2019) stored the anaerobic digestate under psychrophilic conditions (i.e., ambient temperature) before the experiments, hence the residual biogas potential could be considered negligible although they still treated this material, using the biogas as stripping agent, to further remove NH 3 and CO 2 . Following the methodology described by Parra-Orobio et al. (2018), a negative control experiment should be conducted with 150 g of inoculum and 3 g of distilled water (repetitive of the 3 g of pretreated wheat straw) to allow the endogenous correction for the biogas (i.e., discounting the biogas released by the inoculum). According to Walker et al. (2010) and Koch et al. (2020), the negative control experiment should be carried out with the inoculum alone. ...
Developing a suite of biofuels for different applications relies heavily on upgrading technologies to remove nitrogen compounds and carbon dioxide. Particularly in the upgrading of biogas to biomethane, simple water scrubbing is the most widely used technology for biogas upgrading. This technology can be synergistically implemented without the need for additional equipment for processing steps, although this design has not been conceived yet. Samples of biogas-pipeline condensates were collected from 3 different anaerobic digestion plants processing 3 different feedstocks (i.e., food waste, agrowaste, and manure) at 3 different locations in each plant (i.e., biodigester and postdigester condensate pits, digestate pasteurizer, and biogas booster and chiller). The methodology for the analysis of the 5-mL biogas-pipeline condensates was acid-base titration with 0.06 M hydrochloric acid and 0.13 M sodium hydroxide solutions as titrants, and induction of crystallization by cooling at 3 °C, adding up to 40 mL of acetone as antisolvent, and settling for 12 hours. The results showed that the concentration of ammonium bicarbonate in the condensates ranged from 0.75 to 50 g/L. The most suitable location to enhance the upgradation of biogas, formation of condensate, and precipitation of ammonium bicarbonate was the pit after the anaerobic digester and before the biogas storage. The most concentrated condensate was retrieved from the biogas-pipeline coming out of the pasteurization tank, but the operation at 70.5 °C also led to volatilization of organic compounds that negatively affected the biogas quality. Future work aims to investigate coating and granulation of ammonium bicarbonate crystals to improve their stability and commercialization.
... The ADS was kept in porcelain crucibles at 105 • C for 24 h until a constant weight was achieved. Later the oven-dried samples were heated at 550 • C for 4 h in a muffle furnace to measure the VS [18,19]. The ultimate elemental composition (including carbon, hydrogen, sulphur, and nitrogen) and the proportion of metals were measured adopting the procedure and instruments followed in our previous study [20]. ...
Addition of a single additive (such as biochar or calcium) in anaerobic digestion has been studied previously. However, the effect of combined additives in anaerobic digestion (including fat, oil, and grease) has not been well-investigated yet. In this study, the biogas/biomethane, lipid degradation, and volatile fatty acids were investigated under various concentrations of combined additives. The effect on principal reactions, microbial community, and functional enzymes was also analyzed under different concentrations of calcium-modified biochar. The fat, oil, and grease was degraded up to 81.91 % resulting in 9.03-fold higher biomethane production. Acidogenesis and methanogenesis efficiencies were induced up to 53.31 % and 67.91 %, respectively, due to the enrichment of bacteria (such as Clostridium >50 %, Sporosarcina >18 %, Cellulosilyticum >8 %) and archaea (such as Methanosphaera >49 %). Increased abundance of Co-A ligase, short-chain acyl-CoA dehydro-genase, acetate kinase, and formylmethanofuran dehydrogenase, represented mixed hydrogenotrophic and acetoclastic methanogenesis. The current study demonstrated that co-additives can be added to overcome microbial inhibition and facilitate biomethanation at high fat, oil, and grease concentrations.
... These substrates are characterized by their high content of organic matter (VS/TS > 80%) that makes their transformation and recovery through AD viable. [12][13][14][15][16][17] However, there are still challenges to improve in the quality of byproducts such as biogas and digestate for their recovery into value chains. ...
A recently strategy applied to anaerobic digestion (AD) is the use of biochar (BC) obtained from the pyrolysis of different organic waste. The PRISMA protocol-based review of the most recent literature data from 2011–2022 was used in this study. The review focuses on research papers from Scopus® and Web of Knowledge®. The review protocol used permits to identify 169 articles. The review indicated a need for further research in the following challenges on the application of BC in AD: i) to increase the use of BC in developing countries, which produce large and diverse amounts of waste that are the source of production of this additive; ii) to determine the effect of BC on the AD of organic waste under psychrophilic conditions; iii) to apply tools of machine learning or robust models that allow the process optimization; iv) to perform studies that include life cycle and technical-economic analysis that allow identifying the potential of applying BC in AD in large-scale systems; v) to study the effects of BC on the agronomic characteristics of the digestate once it is applied to the soil and vi) finally, it is necessary to deepen in the effect of BC on the dynamics of nitrogen and microbial consortia that affect AD, considering the type of BC used. In the future, it is necessary to search for new solutions in terms of the transport phenomena that occurs in AD with the use of BC using robust and precise mathematical models at full-scale conditions.
... The stimulation of hydrolytic enzymatic activity is another feature of Zn [63,81]. Wang et al. [82] reported that the addition of ZnO nanoparticles at a concentration of 30 mg/g VS enhanced the activities of cellulase, protease, and acetate kinase during the AD of waste activated sludge. ...
The opportunities and challenges of applying micronutrients (MiNs) in full-scale anaerobic digestion (AD) plants has been reviewed. The review discusses the underlying mechanisms and the role of different micronutrients (Fe, Ni, Co, Mo, Zn, Cu, Se) in the enhancement of AD performance, as well as their environmental and economic implications in full-scale AD systems. Bioavailability is a key factor affecting the effectiveness of micronutrients application on the biochemical aspects of AD. Accordingly, the technical aspects of AD with a direct impact on bioavailability have been identified and critically addressed. Mono-supplementation is not the most favorable strategy to increase micronutrient bioavailability due to limited solubility, formation of insoluble compounds, interaction with other compounds, and specific microbial requirements. Nonetheless, co-supplementation can increase the bioavailability due to the simultaneous synergetic effects of co-micronutrients supplementation on the biochemical aspects of AD. However, the inconsistency of reported lab-scale results and the lack of protocols or guidelines for analyzing the bioavailability of micronutrients limit results interpretation and full-scale application. The environmental and economic implications of these micronutrients are other critical factors that need further research. The economic results showed that the mono-supplementation can be economically favorable when a methane enhancement of 20% is achieved. Co-supplementation of micronutrients is the most economically feasible option since this strategy allows reducing the total dosage of micronutrients when compared with mono-supplementation.
... On the other hand, the TP content was low, which is consistent with previous research developed in the study area [49]. In contrast, the TK was high, possibly due to the presence of plantain and banana peels [47,50]. Finally, Mg, which is an essential micronutrient in aerobic processes such as composting, was in the range reported by other authors (<1%) (e.g., [51]). ...
Green waste (GW) represents 11% of municipal solid waste. Managing this waste is challenging due to its physicochemical variability, low density, and presence of hard-to-degrade lignocellulosic compounds. Composting is an alternative for GW transformation and valorization. However, due to the substrate characteristics, processing times are long, and the end product typically does not meet quality standards. Incorporating additives and co-substrates are operational strategies that contribute to overcoming these challenges. An essential step is the determination of a mixture’s composition that ensures synergistic effects on the process and end-product quality. This research assessed the effect of adding biochar (Bch) in the co-composting of GW and food waste (FW). A previously studied co-composting mixture (M) of GW, raw and processed FW, sawdust (Sd), and phosphoric rock (Pr) with four treatments by duplicate were assessed at the pilot scale: T1: 100% GW, T2: M1, T3: M2 + 2% Bch, y T4: M3 + 5% Bch. The results show that Bch treatments maintained the range of thermophilic temperatures for longer than the other two treatments (between four and five additional days), showing greater biological activity and better end-product hygienization. Likewise, in the Bch treatments, the hemicellulose and cellulose degradation improved compared to treatments without Bch by 33.9% and 23.3%, respectively, and nitrogen losses were reduced by up to 70%. Regarding the end product, adding a 2% dose of Bch allowed the highest fertility index compared to the other three treatments, showing its potential for agricultural use. This work demonstrates that adding biochar to FW and GW co-composting improves organic matter degradation rates, lignocellulosic degradation, and end-product quality.
... All measured characteristics of the substrates are tabulated in Table 2 as the average value and standard deviation. Most of the values in Table 2 are consistent with those of previous publications (Alibardi and Cossu, 2015;Baawain et al., 2017;Edwiges et al., 2018;Fitamo et al., 2016;Gallego et al., 2022;Gu et al., 2020;Komilis et al., 2012;Naroznova et al., 2016;Parra-Orobio et al., 2018;Wang et al., 2015). However, the values for certain characteristics may vary due to the definitions of municipal solid waste fraction being distinct and vary, regionally and nationally. ...
Biochemical methane potential (BMP) test is a common technique for determining the methane generation potential (Lo) of substrates at an anaerobic condition. In this study, Lo of seven components of municipal solid waste, namely cooked food waste (CFW), fruit waste (FW), vegetable waste (VW), uncooked food waste (UCFW), paper waste (PW), garden waste (GW), and textile waste (TW) were assessed in a mesophilic condition for 37 days. Beside that, theoretical Lo was predicted based on the organic composition of substrates, the elemental compositions and chemical oxygen demand (COD) of substrates. In addition to that, the biodegradability index (BDI) was calculated to determine the ratio of experimental BMP to theoretical BMP. The findings from the experimental BMP showed that CFW had a greater methane generation potential, which was 328.39 mlCH4/gVS, than TW with 174.02 mlCH4/gVS of methane generation potential. Among all seven substrates, UCFW had the highest BDI, while the lowest organic fraction identified in the current study wasTW. Theoretical prediction for all substrates reveals the overestimation of methane production compared to the experimental method, with a percentage error in the range of 0.08 %–327.02 %. The theoretical BMP method based on COD composition had correction factors ranging from 0.96 to 2.55, while the theoretical BMP method based on elemental composition had correction factors ranging from 0.50 to 4.27. Two models which were the First-order kinetic model (FOKM) and the ModifiedGompertz model (MGM) were utilised in the current study to evaluate the kinetic behaviours of the measured substrates. The results revealed that the MGM fitted the predicted methane generation potential with the highest R2 value (0.96–0.98) and lowest RMSE (8.71–17.20). Therefore, the baseline data can be used to establish potential solutions in municipal solid waste management systems in Malaysia, as well as to provide guidance to waste-to-energy (WTE) parties.
... The combination of Fe, Co, and Ni has been extensively implemented in food waste/wastewater treatment (Ye et al., 2018). These discrepancies may be explained by the fact that various inoculum sources and substrates differ in terms of their inherent TM content (Parra-Orobio et al., 2018). TMs are added to wastewater treatment systems in solution or metal compound particle form. ...
Methanogenic treatment can effectively manage wastewater in the dairy industry. However, its treatment efficiency and stability are problematic due to the feature of wastewater. This review comprehensively summarizes the dairy wastewater characteristics and reveals the mechanisms and impacts of three critical issues in anaerobic treatment, including ammonia and long-chain fatty acid (LCFA) inhibition and trace metal (TM) deficiency. It evaluates current remedial strategies and the implementation of anaerobic membrane bioreactor (AnMBR) technology. It assesses the use of nitrogen-removed effluent return to dilute the influent for solving protein-rich dairy wastewater treatment. It explores the methodology of TM addition to dairy wastewater in accordance with microbial TM content and proliferation. It analyzes the multiple benefits of applying high-solid AnMBR to lipid-rich influent to mitigate LCFA inhibition. Finally, it proposes a promising low-carbon treatment system with enhanced bioenergy recovery, nitrogen removal, and simultaneous phosphorus recovery that could promote carbon neutrality for dairy industry wastewater treatment.
... The anaerobic inoculum used for the BMP test is an important factor for the correct development of the test. The amount of macronutrients and trace elements is an important characteristic which has an impact on the performance of the system, and also affects the methane production [22]. ...
The management and control of food waste is currently seen as a growing concern; anaerobic digestion is a promising alternative for the valorization of food waste. This study evaluates the effect of the application of three pretreatments (grinding, pH control, thermal treatment) and organic load control, employing a high alkalinity inoculum for methane production through BMP tests, using a Taguchi L8 experimental design of 4 factors and 2 levels, resulting in the best performance (65.91 NmL · g-1 TVS) with pretreatment conditions of grinding with fine particle size, pH 11, thermal pretreatment at 60 ∘C and a concentration of 14 g TVS · L-1, which represents an improvement of 34.66% in comparison with the food waste without pretreatments.
Graphical Abstract
... First, the mixing at different inoculum sources increased the community of microorganisms adapted to diverse substrates [10] and promoted the production of biogas and methane. Second, the inoculum source determines the content of macronutrients and trace elements, which can alter the demands of the AD process and affect biogas and methane production [58]. Statistical analysis showed that the methane production of 247.2 NmL CH 4 gTVS − 1 , obtained with the Mix 4 inoculum, was higher (p < 0.05) than that obtained with Mix 2, which was 235.2 Nml CH 4 gTVS − 1 . ...
The inoculum is the initial source of microorganisms for the anaerobic digestion (AD). An active inoculum aids the success of organic matter degradation experiments. Enrichment and acclimation strategies have been studied in search of more efficient tests. The present study aimed to compose an active anaerobic mesophilic inoculum in the laboratory for test standardization. For this purpose, inoculums from different sources available in the study region, such as digested cattle manure (DCM), digested sewage sludge (DSS), digested food waste (DFW), digested swine manure (DSM), fresh cattle manure (FCM), cattle rumen (CR) and some compositions between them were tested in Biochemical methane potential (BMP) assays with microcrystalline cellulose as reference substrate, in addition to fruit and vegetable waste (FVW). The inoculums originated from anaerobic processes showed a greater aptitude for the AD process, being the mixture of DFW, DSM and DCM (Mix 4) presented an abundance of the genus of bacteria DMER64 and Archaeas Methanosaeta, greater production of biogas for the reference substrate, and greater production of biogas and methane for FVW. The aptitude control tests demonstrated that the maintenance of the laboratory reactor with Mix 4 inoculum was efficient. It was evident that the characteristics of inoculum can vary from one collection to another, which validates the fact that the maintenance of an active anaerobic mesophilic inoculum in the laboratory is essential for carrying out AD experiments with standardized and reliable results.
... All the samples were stored at 4 • C for further use. The physicochemical characterization of inoculum, DCO, and FOG was performed by the standard method [12,13]. The total solids (TS) content was determined by heating the samples at 105 • C for 24 h in porcelain crucibles to a constant weight. ...
The efficiency of anaerobic digestion (AD) chiefly relies on substrate composition and microbial structure. The lipidic substrates such as waste cooking oils (WCOs) have high biogas potential. The biogas production from WCOs can be increased by active microbes with simultaneous alleviation of environmental contamination. Thus, this study explored the biogas potential of two different WCOs including duck cooking oil (DCO) and fat, oil, and grease (FOG) in AD. The effects on biogas kinetics, oils degradation, microbial community dynamics, and variations in bacterial and archaeal functional enzymes were investigated. The modified Gompertz and logistic growth models showed a curve-fit within a range of 0.98–0.99 R² value for biogas production in DCO and FOG-loaded reactors. The biogas production was > 5-folds higher in WCOs compared to control. The addition of DCO and FOG showed 76.87 % and 69.76 % of lipid degradation, respectively. The major bacterial enzymes involved in β-oxidation (based on Kyoto Encyclopaedia of Genes and Genomes, KEGG map 00071) of DCO and FOG were acetyl-CoA C-acetyltransferase and enoyl-CoA hydratase. These enzymes correspond to the dominance of Clostridium (>90 %) and might be involved in the formation of biomethane precursors. While the abundance of Methanosphaera (>60 %) and Methanobrevibacter (>30 %) increased the archaeal CoB-CoM reductases and methyltransferase involved in biomethanation. This study demonstrated that the WCOs could be used as potential substrates for biogas production.
... According to the authors, the increase in enzymatic activity may be related to the physicochemical characteristics of the granular sludge (high concentration of TS and VS, which indicate greater organic load and active microorganisms), source of the inoculum (methanogenic reactor) and its property of agglomerating into dense particles (granules). This fact confirms that the mixture of a low quality inoculum (flocculant) with one with better characteristics favors the biological activity and the capacity to transform the substrate into methane (Parra-Orobio et al., 2018b). ...
As food waste gets acknowledged as a global potential source of biomass, its valorization through anaerobic digestion becomes an attractive strategy. This work describes the state-of-the-art on the valorization of food waste by anaerobic digestion and the optimization of the process. The methodology used was a bibliometric and systematic review of the optimization of the process from 66 articles selected. Bibliometric mapping allowed us to identify that, until now, most studies have been focused on the: i) anaerobic co-digestion strategy in order to stabilize the process, ii) interest in the generation of biofuels to replace non-renewable fuels, iii) study of metabolic processes for a better understanding of the system iv) reactor design optimization and others facilities to increase process efficiency. The systematic analysis showed that the operational parameters has been extensively studied to optimize the process. Therefore, co-digestion has been the main strategy to improve the process. In this sense, knowledge of the substrate and co-substrate is extremely important to operate the reactors. For methane production, the ideal operating conditions indicated were: pH of 7, solids content between 4.0 and 15%, C/N ratio of 25, hydraulic retention time from 25 to 40 days and alkalinity from 2850 to 2970.5mgCaCO 3 /L. In addition, the ideal OLR will vary mainly according to operating temperature, number of reactor stages, and raw material characteristics. This review indicates trends and knowledge gaps that are important to guide new research on the anaerobic digestion of food waste, pointing out the potential advantages, optimization strategies, by-products of interest and challenges of the process. The results were used for the development of references of ideal operating conditions for energy production, being able to guide the design and operation of reactors.
... However, the results of this study suggest that it is not the leading cause of inhibition. The iron content of AD sludge is generally 2-3 orders of magnitude higher than that of cobalt and nickel, whereas the iron content in methanogen cells is just over 1 order of magnitude higher than that of cobalt and nickel (Parra-Orobio et al., 2018). From this perspective, the lack of cobalt and nickel will preferentially manifest itself. ...
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The anaerobic digestion (AD) of dairy processing wastewater (DPW) to produce bioenergy is considered promising but also associated with the possibility of an unbalanced organic matter and trace metal (TM) content. In this study, the TM content and its impact on AD were determined in an anaerobic membrane bioreactor operated to treat DPW. The results indicated that a deficiency in TMs resulted in the slow deterioration of the process, reducing biogas production, disrupting the buffer system, and the massive accumulation of organic acid. The deficiency of Co/Ni was significant, while iron fluctuated due to microbial and chemical effects. Syntrophic propionate oxidizing bacteria and methanogen were the main groups suppressed under the TM deficient environment, resulting in AD failure. No inhibitory effect on the lactic acid metabolism was observed. Hence, supplying theoretical TM dosage to DPW was necessary to realize the efficient and stable AD process and robust microbial community.
... The right selection of inoculum is the key factor in the combination of temperature to set a desired AD startup conditions [228,229]. However, the quantity and quality of inoculum can be a major parameter that affects all four phases of AD [230,231]. ...
In recent years, lignocellulosic biomass has gotten a lot of coverage, especially for the captured energy through the anaerobic degradation. The conversion of lignocellulosic biomass to biogas through an anaerobic digestion process has been facing challenges such as low biogas production, low buffering ability, poor end quality of products, and potential heterogeneity of biomass which have difficulties to define an optimized unit operation. These deficiencies may be related to the recalcitrant disposition of agricultural wastes or low mass transfer. India has a large amount of lignocellulosic biomass, and this biomass remains unused in the harvested field. However, it has a scope of utilization by conversion into useful biofuel.
Furthermore, it could be enhanced the farmer's income as well as helps to contribute reduce the loss of environmental impact. Hence, the present review script discusses the potential, composition, biomethane production, pretreatment methods and technology related to lignocellulosic biomass, challenges, progress, and the latest program initiated in India. However, only 10 major types of lignocellulosic biomass have been reviewed in this paper.
... Kim et al. [44] reported an average methane production of 0.27 L CH4 /g VS and 71% of volatile solids reduction during the anaerobic digestion of food waste under mesophilic conditions (35ºC) at a hydraulic retention time (HTR) of 30 d. Parra-Orobio et al. [45] studied the anaerobic digestion of food wastes from a university restaurant in similar conditions as in our study, during 32 d at 35 °C, and achieved methane yields of around 0.137 -0.144 L CH4 /g VS when using a granular sludge from a sugar mill wastewater treatment plant and of around 0.108 -0.149 L CH4 /g VS with a granular sludge from a cattle slaughter treatment process. ...
The aim of this study was to evaluate the theoretical potential of methane production of the food waste generated by a university restaurant, as well as to verify the influence of the fruit and vegetable waste in the feeding composition of an anaerobic bioreactor treating this type of waste. Four feeding compositions combining three fractions of the food waste (fruit and vegetable fraction, soy protein and beans fraction, and rice fraction) at different concentrations were tested in anaerobic processes lasting 10 and 30 days. Additionally, a study of the theoretical potential of methane production from each fraction that composes the food waste was carried out, as well as the evaluation of the specific methanogenic activity of the anaerobic sludge. Despite its low theoretical potential of methane production (0.037 LCH4/g), the presence of the fruit and vegetable mixture in three of the feeding compositions led to greater organic matter degradation (above 69%) and CH4 yields (above 0.20 LCH4/gVS) in both periods tested, in comparison with the achieved by the feeding composition lacking this fraction. The results suggest that the presence of the fruit and vegetable mixture contributed with the supplementation of micro- and macroelements to the anaerobic sludge during the digestion of food waste.
... The higher moisture content recorded for cattle rumen content is useful for its role in ensuring desirable moisture levels during co-digestion (Karki et al., 2021). The values reported here are similar to those reported by Venkateshkumar et al. (2019) for cow dung (86%), Parra-Orobio et al. (2018) for food waste (76%) and Oladejo et al. (2020) for cow dung, food waste and pig dung (85.6%, 81.1% and 81.3% respectively). ...
This study investigated the batch co-digestion of cattle rumen content (CRC) and food waste (FW) for biogas production in different ratios (CRC:FW) to assess biogas production and process stability. The results showed that CRC and FW possess characteristics that are desirable for biogas production as seen in their respective total solids (10.85 and 26.53%), volatile solids (89 and 86.83%) and carbon to nitrogen ratio (23.7 and 15.7) values. Co-digestion improved carbon to nitrogen ratio, biogas yield and pH of the co-substrate compared to individual substrates. The 50:50 co-digestion ratio was found to be optimum as it gave the maximum cumulative biogas yield of 320.52 ml/gVSadded. Co-digestion also improved the pH, volatile fatty acid (VFA) and total ammonia nitrogen (TAN) characteristics during digestion. The cone model was able to adequately represent the kinetics of the process. These findings have provided very useful insights into the co-digestion of CRC and FW.
... The amount of macronutrients and trace elements is an important characteristic which has an impact on the performance of the system, and also affects the methane production. [22] This study aims to evaluate the application of the combined pretreatment process and concentration control on the production of methane generated from the catering industry waste through BMP tests, employing an inoculum with high alkalinity content (higher than 50 g CaCO 3 ·L -1 ). ...
The management and control of food waste is currently seen as a growing concern, anaerobic digestion is a promising alternative for the valorization of food waste. This study evaluates the effect of the application of three pretreatments (grinding, pH control, thermal treatment) and organic load control, employing a high alkalinity inoculum for methane production through BMP tests, using a Taguchi L 8 experimental design of 4 factors and 2 levels, resulting in the best performance (65.91 NmL ·g -1 TVS) with pretreatment conditions of grinding with fine particle size, pH 11, thermal pretreatment at 60 °C and a concentration of 14 g TVS ·L -1 , which represents an improvement of 34.66% in comparation with the food waste without pretreatments.
... The inoculums used in this study were from the same source but collected at different periods from an anaerobic digester treating sewage sludge. As a result, each inoculum sample collected contained different microorganism groups, which influenced the profiles of methane production in each community, resulting in the same pattern of methane production as seen in the methane yield profiles (Parra-Orobio et al. 2018;Wilkins et al. 2015). ...
The ever-increasing organic waste generation in Malaysia is a significant contributor to greenhouse gas (GHG) emissions. However, organic wastes can be utilized to produce biogas by anaerobic digestion, which is a promising option for both energy and material recovery from organic wastes with high moisture content. Therefore, this study was formulated to investigate the feasibility of anaerobic co-digestion of three types of organic wastes generated in significantly huge quantities in Malaysia, namely palm oil mill effluent (POME), food waste (FW), and sewage sludge (SWS). The biomethane potential (BMP) test was used to evaluate the biomethane potential from these organic wastes under mesophilic conditions to establish a stable and balanced microbial community, which may lack in mono-digestion, to improve biogas production. Comparative performance was made at different food to microorganism (F/M) ratios to investigate methane production in three groups of assays, namely A, B, and C. In groups A and B, the effect of F/M ratio variation on methane production was investigated, while in group C, the effect of varying the co-substrate mixture on methane yield was examined. The findings showed that the highest methane yields achieved for mono-digestion of POME and SWS in group A were 164.44 mL-CH4/g-CODadded and 65.34 mL-CH4/g-CODadded, respectively, at an F/M ratio of 0.8 and 197.90 mL-CH4/g-CODadded for FW in group B at an F/M ratio of 0.5. In addition, the highest methane yield achieved from the anaerobic co-digestion was at 151.47 mL-CH4/g-CODadded from the co-digestion of the POME and SWS (50:50) at an F/M ratio of 1.7 in group A. Both AD and AcoD were tested to fit into two kinetic models: the modified Gompertz and the transfer function models. The results showed that the modified Gompertz model had a better fit and was more adjusted to the experimental results for both AD and AcoD. The importance of this research lies in the economics of anaerobically co-digesting these abundance feedstocks and the variations in their characteristics which were found to increase their methane yield and process efficiency in anaerobic co-digestion.
... The start-up of an anaerobic digester is significantly influenced by the quality of the inoculum used, as it plays a crucial role in supplying the reactors with acclimatized microorganisms, as well as the required trace elements [38]. Therefore, to establish the desired anaerobic start-up conditions, the inoculum was collected from a biogas plant treating FW under mesophilic conditions. ...
This study proposed the selection of cost-effective additives generated from different activity sectors to enhance and stabilize the start-up, as well as the transitional phases, of semi-continuous food waste (FW) anaerobic digestion. The results showed that combining agricultural waste mixtures including wheat straw (WS) and cattle manure (CM) boosted the process performance and generated up to 95% higher methane yield compared to the control reactors (mono-digested FW) under an organic loading rate (OLR) range of 2 to 3 kg VS/m³·d. Whereas R3 amended with unmarketable biochar (UBc), to around 10% of the initial fresh mass inserted, showed a significant process enhancement during the transitional phase, and more particularly at an OLR of 4 kg VS/m³·d, it was revealed that under these experimental conditions, FW reactors including UBc showed an increase of 144% in terms of specific biogas yield (SBY) compared to FW reactors fed with agricultural residue. Hence, both agricultural and industrial waste were efficacious when it came to boosting either FW anaerobic performance or AD effluent quality. Although each co-substrate performed under specific experimental conditions, this feature provides decision makers with diverse alternatives to implement a sustainable organic waste management system, conveying sufficient technical details to draw up appropriate designs for the recovery of various types of organic residue.
... Thus, high carbon content residues from crops and rich nitrogen content of animal manure make for an optimal and balanced C/N ratio ). In the same way, the use of an inoculum in AD can have an effect on the speed of the process (Bortolini et al. 2020;Parra-Orobio et al. 2018;Holliger et al. 2016) affecting not only biodegradability but also the CH 4 production rate (Moset et al. 2015;Raposo et al. 2011). Therefore, it is necessary to investigate GP manure digestion performance with other co-substrates and inoculum to observe the effects on biogas production synergy. ...
The objective of this research was to evaluate anaerobic co-digestion of guinea pig manure (GP) with Andean agricultural residues such as amaranth (AM), quinoa (QU) and wheat (TR) in batch biodigesters under mesophilic conditions (37 0C) for 40 days. As microbial inoculum, sewage treatment sludge was used in two inoculum/substrate ratios (ISR of 1 and 2). In terms of methane production, the best results occurred in treatments containing AM and QU as co-substrate and an ISR of 2. Thus, the highest methane production yield in the GP:AM biodigesters (25:75) and GP:QU (25:75) with 341.86 mlCH4/g VS added and 341.05 mlCH4/g VS added, respectively. On the other hand, the results showed that methane production with an ISR of 2 generated higher yields for guinea pig waste and the methane fraction of the biogas generated was in a range from 57 to 69%. Methane production kinetics from these raw materials was studied using five kinetic models: modified Gompertz, logistic equation, transfer, cone and Richards. The cone model adjusted best to the experimental values with those observed with r2 of 0.999 and RMSE of 1.16 mlCH4/g VS added. Finally, the highest biodegradability (experimental yield/theoretical yield) was obtained in the GP-AM biodigesters (25:75) with 67.92%.
... The semicontinuous reactors used for AD of FW were operated under mesophilic conditions (35°C +1°C) and fed with FW from a university restaurant serving 3,000 students daily, generating 86.6 kg of FW per day. The composition of the FW used in this study is based on previous studies by Oviedo-Ocaña et al. (2015) and Parra-Orobio et al. (2018) in small communities that perform separation at the source and selective collection of MSW. The composition of FW used was as follows: banana and potato peels (56%), citrus fruits (25%), non-citrus fruit (8%), fibers and minerals (8%), and herbs (3%). ...
Anaerobic digestion (AD) of food waste (FW) has been gaining more interest as it has potential for the production of organic amendments with high struvite (NH4MgPO4·6H2O) content, which is a nutrient of great interest in sustainable agriculture. In this study, the influence of AD of FW in one- and two-phase configurations on methane production and the potential for struvite formation using digestate was evaluated. It was found that the two-phase is more efficient as its organic loading rate is 18% higher than that of one-phase configuration. In addition, the two-phase yielded a higher methane content in biogas (>60%) and a higher organic matter transformation in each of the AD stages (>20%); further, the digestate complied with the regulatory requirements for the use of organic amendments, thereby being deemed as a Type-B material with a struvite precipitation potential, exceeding 80%, as opposed to the digestate from one-phase configuration, which may represent a revenue of up to US$ 26,505 per year. HIGHLIGHTS
Two-phase anaerobic digestion of food waste (AD-FW) is an alternative for the generation of struvite.;
The presence of struvite helps the sanitization of the digestate obtained in the AD-FW.;
Two-phase AD has potential for the treatment as well as energy and agricultural use of FW in small communities.;
... The start-up of an anaerobic digester is significantly influenced by the quality of the inoculum used as it plays a crucial role in supplying the reactors with acclimatized microorganisms as well as the required trace elements (TEs) [40]. Therefore, to set a desired anaerobic start-up condition, the inoculum was collected from a biogas plant treating FW under mesophilic conditions. ...
Tunisia is one of the developing countries which faces crucial challenges, the most prominent of which are the production of organic waste, the need for an appropriate waste treatment, and the demand for water and energy conservation. To this end, the present research was designed to develop a technical concept on closed cycle “biowaste to bioenergy” treating food waste (FW) through combined biological processes. In this approach, semi-continuous anaerobic co-digestion (ACoD) of FW, wheat straw (WS), and cattle manure (CM) was tested to investigate the relationship between the effect of the feedstock mixtures and C:N ratio on biogas and digestate generation at different organic loading rates (OLRs) ranging from 2 to 3.6 kg VS/m ³ .d. Results showed that the mono-digested FW was optimal and reached 565.5 LN/kg VS in at an OLR of 2.4 kg VS/m ³ .d, and then a drop of biogas production was recorded. However, for co-digested substrates, the optimum mixture ratio was FW:CM 75:25, where 62%, 39.89%, 91.26%, 130.9%, and 119.97% of the biogas yield improved for OLRs ranging from 2 to 3.6 kg VS/m ³ .d, respectively. Admittedly, the target of this work was to enhance the ACoD process, but it also examined the exploitation of different AD effluents. Therefore, special attention was paid to the generated digestates to decide how it can be efficiently upcycled later. Thus, the closed cycle “biowaste to bioenergy” treatment met two of the major Tunisian concerns: efficient organic waste management and sustainable bioenergy production.
... Biomethane production from organic matter relies on the quantity and quality of inoculum added in AD reactors, determined by TS, VS, and elemental composition [12]. The main physicochemical properties of different ADSs collected from WWTP at different periods presented in Table 1. ...
Anaerobic digestion (AD) is a biological process, encompasses the treatment and stabilization of complex organic matter to extract renewable biomethane fuel through microbial interaction in the digester. The main aim of the current study is to investigate the microbial community of anaerobic digestion sludge (ADS), collected at different periods from a mesophilic operating anaerobic digester. The core group of bacteria in ADS including Firmicutes, Bacteroidetes, and Proteobacteria represented more than 60% of the core bacterial community. In ADS (I), the supremacy of Cloacimonetes (18%) was also observed. In ADS (II), the dominance of Anaerobacter (8%) showed the effect of substrate composition on the microbial structure. However, 91% relative abundance of Firmicutes was observed in ADS (III). The hydrogenotrophic methanogens belonging to order Methanomicrobiales and Methanobacteriales exhibited dominance in all three ADSs (> 60%). No specific variations in the archaeal community might be attributed to the presence of beneficial bacterial species. This study provides all the detailed functional roles of microbes involved in AD which can further be used for additional environmental applications.
... Thus, the high carbon content of the residues from crops and the rich nitrogen content of animal manure make for an optimal and balanced C/N ratio . In the same way, the use of an inoculum in AD can influence the speed of the process (Bortolini et al., 2020;Parra et al., 2018;Holliger et al., 2016) affecting not only biodegradability but also the CH4 production rate (Moset et al., 2015;Raposo et al., 2011). Therefore, it is necessary to investigate the performance of CY manure digestion with other co-substrates and inoculum to observe the influence of biogas production synergy. ...
The objective of this research was to evaluate the anaerobic co-digestion of guinea pig manure (CY) with Andean agricultural residues such as amaranth (AM), quinoa (QU) and wheat (TR) in batch biodigesters under mesophilic conditions (37⁰C) for 40 days. As microbial inoculum, sewage treatment sludge was used in two inoculum/substrate ratios (ISR of 1 and 2). In terms of methane production, the best results occurred in the treatments that contained AM and QU as co-substrate and an ISR of 2. Thus, the highest methane production occurred in the CY:AM biodigesters (25:75) and CY:QU (25:75) with 341.86 mlCH 4 /g VS and 341.05 mlCH 4 /g VS, respectively. On the other hand, the results showed that methane production with an ISR of 2 was more feasible for guinea pig waste, where the methane fraction of the biogas generated was in a range of 57 and 69%. The kinetics of methane production from these raw materials was studied using five kinetic models: modified Gompertz, logistic equation, transfer, cone, and Richards. The cone model was the one that best adjusted the experimental values with those observed with an r ² of 0.999 and an RMSE of 1.16 mlCH 4 /g VS. Finally, the highest biodegradability was obtained in the CY-AM biodigesters (25:75) with 67.92%.
... Overall, although the biomass established a metabolic pathway that favoured acetic acid production, the alkalinity rates reflected that the reactor exhibited disturbances and inhibition due to the presence of substances such as LCFA (Guo et al. 2018) (Figure 2-Supplementary; Table 1-Supplementary). This effect can be attributed to aspects such as the better adaptation conditions for the mixed inoculum used in this study, which can provide biomass with a greater assimilation capacity for the substrate evaluated (Parra-Orobio et al. 2018b). ...
The high organic content of food waste (FW), which represents the largest proportion of municipal solid waste (MSW) (in Latinamerican countries 50-75%), makes its treatment increasingly common trough technologies such as anaerobic digestion (AD), to obtain value-added by-products, such as renewable energy in the form of methane, digestates and other by-products of biotechnological applications such as long-chain fatty acids. In this study, the influence of semi-continuous reactors in single-stage (R1) and two-stage (R2: acidogenic and R3: methanogenic reactors) configurations on the AD-FW was evaluated (including parameters related to process monitoring, organic matter conversion and process reactions) with the following organic loading rate (OLR: kgVS m-3 d-1) values: i. R1: 0.7, 1.5, 3.0 and 6.0; ii. R2: 3.0, 4.0, 9.0 and 15.0; and R3: 1.0, 2.0, 4.0 and 7.0. The two-stage configuration showed a better performance in terms of: i. the OLRs: 35% higher than that in the single-stage configuration, with chemical oxygen demand (COD total) and volatile solid (VS) removal efficiencies > 80%; ii. the best performance in terms of methane production, with statistically significant differences (p<0.05) in the quantity and quality of biogas and iii. obtaining other by-products with high added value, such as behenic and caproic acid, which are useful in biotechnological applications. Additionally, it was found that total reducing sugars (TRS) are an important parameter in the monitoring and conversion of matter organic, mainly in two-stage configuration.
There is a growing recognition that food waste (FW) comprises a significant amount of unused energy. Indeed, FW shows great potential to produce methane (CH4)-rich biogas via an anaerobic digestion (AD) process. Nevertheless, to ensure high AD process performance, deepening the knowledge of FW characteristics is required. Furthermore, the biogas yield is strongly influenced by several operational parameters. Taking into account the above, in the current study, based on the data in the literature, the physicochemical parameters of FW generated throughout the world are presented and discussed. In addition, the performance profile of the single-stage anaerobic mono-digestion process with the use of FW as a feedstock was investigated. The performed analysis clearly demonstrated that FW is characterized by significant variations in several parameters, such as pH, the total solid (TS) and volatile solid (VS) contents, the volatile solids to total solids ratio (VS/TS), soluble chemical oxygen demand (sCOD), the concentrations of VFAs and ammonium nitrogen (NH4⁺-N), and the carbon-to-nitrogen ratio (C/N). Moreover, it was shown that the selected operational parameters, such as temperature, pH, the ratio of food waste to inoculum (I) (FW/I), and the organic loading rate (OLR), may have the most significant impact on the performance of the single-stage anaerobic mono-digestion process. In addition, it was found that most of the experimental investigations presented in the literature were conducted on a laboratory scale. Hence, in future research, more effort should be made to determine the biogas yield with the use of full-scale systems. To summarize, it should be clearly highlighted that the analysis presented in this study may have important implications for the management and application of FW as feedstock for an anaerobic mono-digestion process on an industrial scale.
A Biofilter is a simple technology used in an anaerobic baffled reactor (ABR) to keep biological solids (inoculum) from being easily carried by the inlet substrate and to shorten the hydraulic retention time (HRT). The principle of a biofilter is to form a biofilm on the packed bed of the biofilter in ABR so that it contains immobilised microorganisms. This study aims to know the performance of the biofilter reactor on biogas production during the acclimatisation process. The results show biofilters shorten the HRT and effectively remove pollutants, increasing biogas production and methane quality. The total solid content decreases by around 44%, from 0.38% to 0.17%. The biogas production during acclimatisation was 1806.41 L and COD removal was 95%. The biogas composition of CH4 was 58.05%, CO2 38.23%, and N2 3.2%. This study provides preliminary findings for further studies on the use of tofu wastewater as a biogas feedstock with different concentrate substrates, which is very useful for sustainability activities and improving the industry to become green.
The mechanical pre-treatment constitutes an unavoidable pre-step prior to biofuels conversion. As the cost of this step is often underestimated, recently researchers have striven to identify and characterize the mechanical pre-treatment effects in terms of post-treatment physical characterization, derived improvement of enzymatic digestibility, and output yields. The status of existing mechanical pre-treatment techniques is reviewed by substrate’s typology for lignocellulose biomass, focusing on comminution techniques. Emphasis has been dedicated to the particle size achieved after treatment, crystallinity breakage and eventual inhibitory phenomena deriving from the application of particle size reduction, which are analysed and discussed.
The mechanical pre-treatment constitutes an unavoidable pre-step prior to biofuels conversion. As the cost of this step is often underestimated, recently researchers have striven to identify and characterize the mechanical pre-treatment effects in terms of post-treatment physical characterization, derived improvement of enzymatic digestibility, and output yields. The status of existing mechanical pre-treatment techniques is reviewed by substrate’s typology for lignocellulose biomass, focusing on comminution techniques. Emphasis has been dedicated to the particle size achieved after treatment, crystallinity breakage and eventual inhibitory phenomena deriving from the application of particle size reduction, which are analysed and discussed.
With the aim of evaluating the environmental economic value of Biocell technology, in this paper, excavated waste residue (EWR) from the Calgary Biocell was characterized for the first time. The objective was to find the carbon offset of the Calgary Biocell project through biochemical methane potential (BMP) assay. The EWR samples were collected from different locations within the Calgary Biocell, and the physical and chemical characteristics of the individual EWR samples were evaluated following the standard methods. The BMP assays were conducted using the modified solid-phase method that represent condition of landfills more accurately. A composite sample which was a mixture of all EWR samples was prepared to represent the entire Biocell condition. Laboratory batch experiments were conducted using the biodegradable fraction of EWR to evaluate the methane (CH4) generation potential (Lo) and the first-order rate coefficient (k) values of Calgary Biocell. Based on the BMP assays, it was shown that the excavated waste from the Calgary Biocell has gone through more degradation (i.e., with a production of 16.81 ± 2.9 mL CH4/g TS) compared with the other studies on excavated waste, emphasizing effectiveness of Biocell technology in terms of waste degradation.
Biogas reactors operating with protein-based biomass have a high methane potential and industrial value. Protein-rich materials, including gelatin processing and ossein factory waste, are suitable feedstocks for use in ammonia-tolerant biogas digesters. However, the anaerobic digestion of these materials is limited by the accumulation of ammonia, hydrogen sulfide, and lactic acid. A stable biogas starter is required for efficient biogas production from protein-based mass and process performance. Hence, various ammonia-tolerant biogas inocula, immobilization carriers used, culture formulations, and stater stability are comprehensively summarized in this review. We also discuss engineered methanogens and mutants to improve methane productivity. The genera Methanoculleus and Methanosarcina are the dominant ammonia-tolerant methanogens studied in different biogas plants; however, their ammonia-tolerant molecular mechanisms remain unclear. Recent advances in omics technologies, systems, and synthetic biology of methanogens have been reviewed and discussed for the design and development of methanogenic inocula. We described the genome-centric characteristics of methanogenic consortia to improve the process efficiency under the desired environmental conditions. We also focus on the perspective of methanogenic culture development for the co-production of acetone–butanol–ethanol and methane as well as odor control strategies. A novel metabolic scaffold “Protein Catabolism-Directed Methanogenesis” was discovered from a methanogenic culture using a systems biology approach. This review offers new insights into the feasibility of ammonia-tolerant biogas starters and engineering synthetic pathways for recycling gelatin processing waste into biofuels in the energy sector.
Food waste is an attractive feedstock for Anaerobic Digestion due to its high biodegradability and moisture content. Nevertheless, due to its complex structure and composition, methane yield is typically compromised with 50-60% of the theoretical maximum obtained. The well-known limitation of the hydrolysis step can be circumvented by adopting feedstock pre-treatments, such as microwave irradiation. It improves solubilization of various FW components making them more readily available for the microorganisms and reducing AD process duration. In this work different heating rates (7.8, 3.9 and 1.9 °C/min) and temperatures (85, 115, 145, 175 °C) were applied when pre-treating food waste as a substrate for AD. Increase in the solubilization of organic matter in the form of Soluble Chemical Oxygen Demand was the most significative change in FW characteristics after pre-treatment, with final temperature of 175 °C and heating rate of 3.9 °C showing a 73.19% increment. Nevertheless, process performance of AD of MW FW was optimum at 85 °C 7.8 ramp, showing no intermediate products accumulation, up to 77% more methane produced in the first week of digestion compared to the other conditions tested and reduction of 96.36% on the lag phase duration, compared to the control. On the other hand, samples treated at 175 °C, regardless of heating rate, consistently showed poor process performance, with low methane yield, possibly due to the formation of hard-to-digest compounds. This work underlines the importance of adjusting microwave temperature and power when pre-treating FW for biomethane production so the process is optimized.
The organic fraction of municipal solid waste is mainly composed of food waste (FW), and traditional disposal practices for this fraction are generally considered to have negative environmental and economic impacts. However, the organic characteristics of this fraction could also be exploited through the anaerobic digestion of FW (FW-AD), which represents unique advantages, including the reduction of the area required for final disposal and environmental pollution and the same time the generation of renewable energy (mainly methane gas), and a by-product for agricultural use (digestate) due to its high nutrient content. Although approximately 88% of the world's population resides in areas with temperatures below 8 °C, psychrophilic conditions (temperatures below 20 °C) have hardly been studied, while mesophilic (66%) and thermophilic (27%) ranges were found to be more common than psychrophilic FW-AD (7%). The latter condition could decrease microbial activity and organic matter removal, which could affect biogas production and even make AD unfeasible. To improve the efficiency of the psychrophilic FW-AD process, there are strategies such as: measurement of physical properties as particle size, rheological characteristics (viscosity, consistency index and substrate behavior index), density and humidity, bioaugmentation and co-digestion with other substrates, use of inocula with psychrophilic methanogenic communities, reactor heating and modification of reactor configurations. However, these variables have hardly been studied in the context of psychrophilic conditions and future research should focus on evaluating the influence of these variables on FW-AD under psychrophilic conditions. Through a bibliometric analysis, this paper has described and analyzed the FW-AD process, with a focus on the psychrophilic conditions (
With the rise of fuel-related environmental and economic problems, clean and renewable sources of energy are being developed. In this chapter, we will discuss the valorization of biogas, produced by methanation of organic waste, in the dry reforming of methane reaction. First of all, an overview of the methanation process, the composition, and the valorization of biogas is presented. Then, the dry reforming of methane reaction is discussed, with an emphasis on the deactivation mechanisms by reoxidation, carbon formation, sintering, and poisoning. Third, an overview of the different parameters influencing the catalytic performance is reported. The focus will be on the material composition, the method of synthesis, and the reaction conditions such as temperature, pressure, inlet gas composition, and flow rate. This work aims to present an overview of the recent progress made in the field of waste valorization and renewable energy production.
Application of anaerobic digestion (AD) has become common in treating palm oil mill effluent in Malaysia; however, employing AD in treating the organic fraction of municipal solid waste (OFMSW), especially food waste, is still scarce. This study aims to characterize the commercial Malaysian food waste (CMFW) and determine its potential as sustainable bioenergy feedstock through biogas production. The sample was digested via the biomethane potential (BMP) test with the variation of organic loading rates (OLRs), ranging from 0.38 to 3.83 gCOD/L. day, under mesophilic conditions. The digestion process was further evaluated in continuous operation using a 6-L continuous stirred-tank reactor (CSTR). The kinetic properties of the process were also determined. It was found that the CMFW had a significant amount of chemical oxygen demand of 230 g/L and an acidic pH of 4.5 with the carbon to nitrogen (C/N) ratio at 121:1. A maximum methane composition of 81% was obtained at 1.92 gCOD/L in the BMP test with specific methane production (SMP) at 0.952 L. CH4/L.COD fed. The biogas production was well-fitted with the modified Gompertz model with R ² at 0.9983 and the maximum biogas potential production rate at Rm 0.1573 L/day, whereas in the CSTR operation, a maximum methane composition of 85% was produced at OLR 6 gCOD/L. day with the SMP of 1.13 L. CH4/L.COD fed. The CSTR system was in high stability as the pH was maintained in a range of 6.6–6.7, with an alkalinity ratio of 0.28. This study indicates the CMFW is a sustainable feedstock for biogas production in Malaysia. Toward a circular economy approach, the authorities shall introduce commercial scale CMFW AD as part of managing municipal solid waste issues in Malaysia.
Dans le contexte environnemental et énergétique actuel, beaucoup de recherches sur la production d’énergies renouvelables sont développées. Ce projet s’inscrit dans le cadre de la valorisation des déchets recyclables en collaboration avec un centre d’enfouissement (Opale Environnement). Dans un premier temps, le biogaz produit par méthanisation est prélevé et analysé. Les composés majoritaires (CH4 et CO2) et les composés minoritaires (soufrés, azotés, aromatiques, terpènes et hydrocarbures) sont identifiés et quantifiés. Ensuite, la valorisation du biogaz à travers la réaction de reformage à sec du méthane en présence de catalyseurs Co-Ni-Mg-Al est étudiée. L’efficacité de cette série de catalyseurs est suivie en absence ou en présence d’impuretés ajoutées à un mélange synthétique et stoechiométrique de CH4 et CO2. Enfin, un biofiltre fongique est développé dans le but d’éliminer le H2S présent dans le biogaz. La capacité de champignons filamenteux à métaboliser le H2S gazeux est étudiée via un système de purification biologique.
Anaerobic digestion has been adopted as a potential tool to resolve the menace of unrestrained food wastage. The inherent characteristics of food makes food waste inevitable. Food waste, high in biodegradability, rich in nutrition, and with suitable intrinsic characteristics, reveals its competency as a potential substrate for anaerobic digestion. Though food waste as a substrate is fortuitous, its anaerobic digestion confronts few challenges and necessitates to be resolved to achieve optimal efficiency. Food waste anaerobic digestion is an intricate process and requires continuous monitoring and maintenance of the critical operating parameters. This chapter deals with the critical parameters to be scrutinized and controlled to achieve desirable process stability and performance. The influence of the process performance and efficiency with respect to the substrate characteristics, reaction temperature, pH, organic loading rates, and hydraulic retention time are discussed by providing insights on their critical limits. Techniques such as codigestion to improve the nutrient balance, process stability and stage separation to handle higher organic loading rates at reduced hydraulic retention times are significant considerations for managing anaerobic digestors with deficient substrates. The strategies to enhance the performance of the food waste anaerobic digestion, trends in biogas upgradation and potential opportunities to improve the pecuniary benefits of the process has been discussed in this chapter.
The ever-increasing organic waste generation in Malaysia is a significant contributor to greenhouse gas (GHG) emissions. However, organic wastes can be utilized to produce biogas by anaerobic digestion, which is a promising option for both energy and material recovery from organic wastes with high moisture content. Therefore, this study was formulated to investigate the feasibility of anaerobic co-digestion of three types of organic wastes generated in significantly huge quantities in Malaysia, namely palm oil mill effluent (POME), food waste (FW), and sewage sludge (SWS). The biomethane potential (BMP) test was used to evaluate the biomethane potential from these organic wastes under mesophilic conditions to establish a stable and balanced microbial community, which may lack in mono-digestion, to improve biogas production. Comparative performance was made at different food to microorganism (F/M) ratios to investigate methane production in three groups of assays, namely A, B, and C. In groups A and B, the effect of F/M ratio variation on methane production was investigated, while in group C, the effect of varying the co-substrate mixture on methane yield was examined. The findings showed that the highest methane yields achieved for mono-digestion of POME and SWS in group A were 164.44 mL-CH4/g-CODadded and 65.34 mL-CH4/g-CODadded, respectively, at an F/M ratio of 0.8 and 197.90 mL-CH4/g-CODadded for FW in group B at an F/M ratio of 0.5. In addition, the highest methane yield achieved from the anaerobic co-digestion was at 151.47 mL-CH4/g-CODadded from the co-digestion of the POME and SWS (50:50) at an F/M ratio of 1.7 in group A. Both AD and AcoD were tested to fit into two kinetic models: the modified Gompertz and the transfer function models. The results showed that the modified Gompertz model had a better fit and was more adjusted to the experimental results for both AD and AcoD. The importance of this research lies in the economics of anaerobically co-digesting these abundance feedstocks and the variations in their characteristics which were found to increase their methane yield and process efficiency in anaerobic co-digestion.
The anaerobic digestion (AD) of organic fractions of municipal solid waste (OFMSWs) represents a promising solution for achieving greater landfill diversion and resource recycling. The objectives of this study were (1) to explore potential synergistic effects on methane production of co-digestion of organic MSW components with distinct levels of biodegradability and (2) to examine whether and how the inoculum source affect those synergistic effects on methane yields and kinetics. Anaerobic mono- and co-digestion of food waste (FW), newsprint paper (NP), and branches (BR) were conducted in a batch culture system inoculated with landfill leachate and anaerobic sludge under mesophilic conditions. The methane generation results showed that co-digestion of readily degradable FW with more recalcitrant lignocellulosic NP and/or BR resulted in additive effects on cumulative yield but synergistic effects on production rates (up to 22% yield increase between 10 and 15 days). This early synergism was primarily associated with the accelerated hydrolysis due to the addition of FW that promoted the growth of hydrolytic microorganisms. A 16S rRNA sequencing-based community analysis revealed that the microbial communities were primarily influenced by their inoculum and cannot explain for the observed synergy. These results suggest that when multi-component municipal waste is used as AD feedstock, the early synergistic benefits can be considered for process design and optimization.
To investigate how the seed microbial community structure affects the improvement of methanogenesis efficiency through direct interspecies electron transfer (DIET), a biomethane potential (BMP) test was conducted using sludge collected from a total of six anaerobic digesters. DIET-stimulating microbial populations were investigated by 16S rRNA gene sequence analysis. Correlations between microbial community composition and methane production performance by DIET were analyzed. The methane production rate increased under all conditions when granular activated carbon (GAC) was injected regardless of the inoculum type. However, redundancy analysis indicated a significant correlation between the inoculum microbial community and lag time. In a network analysis, Methanolinea species distributed in the inocula formed a single modularity with lag time, suggesting that the methanogens in the inocula might reduce the lag time of methanogenesis through DIET. Overall, this study revealed that the inoculum microbial community composition is an important factor affecting methane production efficiency by DIET.
The aim of this work was to provide solid proofs regarding the achievement of “steady-state conditions”, which means that the performance of the anaerobic digester is representative of the applied environmental conditions. For this reason, we investigated how, starting from different inoculum sources (i.e., municipal wastewater treatment, bio-waste treatment, and agricultural waste biogas plant), the microbial community adapted to the operational parameters and led to stable biogas production in thermophilic digesters treating the same influent feedstock. The results revealed that the different system achieved similar process performance and microbial community structure after a period that was equal to four hydraulic retention times, approved by a constant pH of 7.89±0.08, 7.92±0.05 and 7.85±0.08, respectively, and stable TAN concentration of 1500 mg/L. Moreover, it was found that the microbial composition of the inocula was a key factor for the speed of achieving stable process performance; thus, a pre-adapted to the influent feedstock inoculum can shorten the stabilization process. On the contrary, after long term reactor operation, the microbial structure was shaped according to the chemical composition of the influent feedstock. The results of the study can also be used as a guide in future researches on anaerobic degradation, particularly in determining the time interval of an experiment to reflect changes in the microbial community of anaerobic digester.
Anaerobic digestion is a biological process that achieves two purposes simultaneously, waste treatment to control environmental pollution and the recovery and valorization of by-products generated: methane as a source of renewable energy and digestate for agricultural purposes. To determine the methane production capability, the anaerobic biodegradability of an organic substrate, the selection of potential substrates and inoculums and the performance prediction of full-scale digesters, bench scale procedures as Biochemical Methane Potential (BMP) test, are performed. This article shows a reflection on different aspects related to this important test, such as the diversity in the experiment denomination, the different modifications in operational and experimental conditions, the different use of measurement units, the required equations for methane quantification, among others, these have given place to various methodological approaches which differ in conditioning factors for its application and comparison with results of other studies. With this reflection, the usefulness of this assay and the need to standardize it is ratified. Therefore, the experimental and operational conditions and the appropriate units should be reported, to avoid methodological confusion and permit a greater reproducibility. Additionally, it is recommended to deepen in the methodological analyses of different measurement methods to obtaining comparable results.
Production of biogas from different organic materials is a most interesting source of renewable energy. The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. A workshop was held in June 2015 in Leysin Switzerland to agree on common solutions to the conundrum of inconsistent BMP test results. A discussion covers actions and criteria that are considered compulsory ito accept and validate a BMP test result; and recommendations concerning the inoculum substrate test setup and data analysis and reporting ito obtain test results that can be validated and reproduced.
The residues enriched in putrescible materials and those with a high content of organic fraction produce large environmental impacts and other problems associated with the productive sector where they are generated. Colombia has a high biomass potential susceptible to be energetically valorized through biological processes achieving two functions: treatment and energy production. Anaerobic digestion is established as a technology with worldwide applications inside the circular biobased economy concept (cradle to cradle). Nevertheless, most of the studies related to technologies like anaerobic digestion have been concentrated on residues from industrialized countries. Considering the variability of residues composition depending on the level of development of a country, it is necessary to assess the biomethanation potential of biomass produced by different productive sectors in Colombia. In this study, a biomethanation potential assessment of organic residues (Organic Fraction of Municipal Solid Wastes, swine manure, cocoa husks and pods, residues from the bottled fruit drinks industry and rice stovers) from different productive sectors in Colombia was carried out. The biochemical methane potential (BMP) of each residue and its mixtures was carried out in a system which consisted in a battery of batch reactors (250 and 120 mL bottles) equipped with gasometers. To keep mesophilic conditions, an immersion thermostated bath was used. For all mixtures, an optimum C/N ratio of 20-30 was fixed based on the previous physicochemical characterization of the employed residues. The batch digestion process was evaluated until the total stoppage of gas production. The results indicate that the best mixture in terms of biogas production is the one containing cocoa, fruits and swine manure (C/N = 24), reporting a cumulative specific gas production around 497 mL CH4/g VS. However, this result was lower than the sum of the ones reported by BMP for each individual substrate.
In this work we studied the decomposition of organic matter of food kitchen wastes (substrate) by sewage sludge (inoculum) from a wastewater treatment plant, through the process of anaerobic digestion (AD) in order to obtain biogas and to determine the biochemical methane potential (BMP) at the end of this process. The tests were performed with substrate:inoculum ratios 1:2 and 1:3, in terms of volatile solids (VS). The most important parameters that influence AD were VS, total solids (TS), chemical oxigen demand (COD) and pH. They were measured in the course of the process in mesophilic conditions (35 °C) and retention times of 15 days. The biogas obtained was purified by removing H2S and NH3 with NaOH and H2SO4 traps. For experiments with inoculum and substrate, 1.235 L of biogas with 80.15% CH4 were recovered and for tests without substrate, 0.720 L of biogas with 90.47% of CH4 were gathered. The quantification of this gas was performed by gas chromatography. The results agree with biogas production and organic load decrease, expressed as COD. For experiments S:I, the BMP values obtained were 124.82 and 127.89 mL CH4/g VS, for 1:3 and 103.39 and 116.27 mL CH4/g VS for 1:2. © 2016, Centro de Ciencias de la Atmosfera, UNAM. All rights reserved.
A laboratory scale two-stage anaerobic process was studied in order to treat biodiesel wastewater. The first stage
represented an acidogenic reactor while the second stage was a methanogenic reactor. The effect of nitrogen and phosphorus
on the performance of both reactors was investigated. Biodiesel wastewater was adjusted so that its COD:N and COD:P
within 100:0.1–1.1 and 100:0–1, respectively, and fed into the acidogenic reactor. After COD and pH adjustment, wastewater
discharged from the acidogenic reactor was fed into the methanogenic reactor. The highest VFA concentration of 8.32 g/l was
obtained from the acidogenic reactor at COD:N:P of 100:1.1:0.5. However, the highest CH4
yield of 0.170 l CH4
/g CODremoved
was found at COD:N:P of 100:0.6:0.5 from the methanogenic reactor. Moreover, both nitrogen and phosphorus affected the
acid composition produced in the acidogenic reactor and the long chain fatty acid consumption in the acidogenic and
methanogenic reactors.
En los países en desarrollo, los biorresiduos son la fracción predominante de los residuos sólidos municipales (RSM); los biorresiduos tienen un alto contenido de materia orgánica, característica que favorece su transformación a través de procesos biológicos como la digestión anaerobia (DA). En este estudio, mediante ensayos de potencial bioquímico de metano (PBM), se evaluó la influencia de la relación sustrato-inóculo (S/I) sobre la DA de biorresiduos de origen municipal (BOM), utilizando relaciones de 0.25 a 9 gSVsustrato*gSVinóculo-1. Como inóculo se empleó lodo de un biodigestor anaerobio de una planta de tratamiento de aguas residuales domésticas. Se encontró que la relación S/I tiene efecto sobre la DA de los BOM (p < 0.1), en donde la relación 0.25 produjo los mejores resultados (producción de 176.19 mLCH4*gSV-1 y un índice de biodegradabilidad de 73.12%, mientras que la relación de 9 generó los más bajos resultados (17.56 mLCH4*gSV-1 y 7.29%, respectivamente). También se encontró que las relaciones S/I menores de 2 gSVsustrato*gSVinóculo-1 permiten un proceso adecuado; con valores mayores, el proceso se desestabiliza debido a la ocurrencia de procesos de acidificación por la acumulación de los AGV's que no logran estabilizarse por la baja capacidad buffer del sistema.
This paper presents a review on the different methodologies to determine the specific methanogenic activity (SMA) of anaerobic sludges. The protocols available in the literature differ not only regarding the procedures adopted to incubate the sludge, but also in relation to the method utilized to quantify the methane produced during the test. This paper discusses the principles of manometric and volumetric methods, and briefly describes the protocols mostly used by the Brazilian research community for sludge incubation, methane measurement and calculation of SMA.
Hydrogen sulfide generation in oil production is a constant cause of concern. In several cases this phenomenon occurs due to the action of sulfate-reducing bacteria. Various methods, including biocides and nitrate addition, have been used to control the activity of these microorganisms, but they are expensive and have side effects. Other inhibition methods, such as the use of molybdate, have received much less attention. This study performed a kinetic test for the inhibition of sulfate reduction, and short-term tests to determine the minimum inhibitory concentration of molybdate in liquid medium containing 10.4 and 20.8 mM of sulfate (1000 mg L-1 and 2000 mg L-1), respectively. An inoculum was prepared from a microbial consortium of sulfate-reducing bacteria dominated by Desulfovibrio vulgaris enriched from produced water from oil wells of the Reconcavo Basin, Brazil. The indicators of bacterial activity used were: sulfate reduction, sulfide production, culture medium color, pH, and redox potential. The tests show that, regardless of the concentration of molybdate, sulfate reduction is inhibited after the first hours of the start of the test. The conversion of sulfate in the kinetic experiment without molybdate is 78%, whereas the average conversion in the experiment with molybdate is approximately 30% in 216 h. The short-term test results show that 0.08 mM (12.8 mg L-1) molybdate, a molar ratio molybdate/sulfate of 0.004, is sufficient to inhibit the activity of sulfate-reducing bacteria for 168 h.
Los biorresiduos de origen municipal-BOM, se caracterizan por su alto contenido de materia orgánica, humedad y nutrientes, además de ser residuos fácilmente acidificables, lo que los convierte en una fuente contaminante cuando se disponen inadecuadamente. La digestión anaerobia-DA es una
alternativa tecnológica para el control de la contaminación de los BOM y la obtención de una fuente de energía renovable, como el metano; sin embargo, variables, como el pH, pueden afectar el proceso. Este estudio evaluó, a escala de laboratorio, mediante ensayos de Potencial Bioquímico de
Metano-PBM, a una temperatura de 30oC, durante 40 días, la influencia del pH sobre la DA de BOM. Los valores de pH del sustrato variaron entre 5,5 a 8,0 unidades, utilizando como inóculo lodo, proveniente de la biodigestión anaerobia de lodos, de una planta de tratamiento de aguas residuales
domésticas. Se evidenció que los pH ácidos correspondientes a 5,5 y 6,0 unidades, presentaron la menor producción de metano, del orden de 70,0 y 71,0 mLCH4*gSV-1, respectivamente, mientras que los pH cercanos a la neutralidad, lograron los mejores resultados, siendo la producción a un pH
de 7,0 unidades la mayor, la cual, fue 126,0mLCH4*gSV-1.
Los resultados están acordes con el comportamiento de la capacidad buffer, que fue más adecuada, entre 7,0 y 8,0 unidades, garantizando estabilidad del proceso anaerobio y evitando así la ocurrencia de fenómenos de inhibición. Para lograr estos niveles de pH, se hace necesario adicionar un
alcalinizante, debido a las características ácidas de los BOM.
One key factor in reactor start-up is inoculum seed. Normally, the indigenous seed is used; however, it is not available near the new biogas plant. The exogenous seed from different wastes treatment system should be considered. This study selected inoculum seeds and wastewaters from various agro-industrial wastewaters based on carbohydrate, lipid and protein manufacturers including a concentrated rubber factory (RB), cassava starch factory (CS), palm oil mill factory (PO), swine farm (SW) and soymilk processing factory (SM). A 5 x 5 inoculum seeds and a wastewaters factorial experimental design were investigated in batch operation mode at an organic loading of 2 g COD l-1 and 37 °C incubation. The results showed that all of the inoculum seeds can be used to degrade the exogenous wastewaters to methane. It was noted that the inoculum seeds can be applied to other sources of wastewater. The efficacy of inoculum seeds to start-up the anaerobic reactor depends on the initial activity and biodegradability of wastewater composition.
The effect of adding four minerals as micronutrient sources to stimulate the anaerobic process of
microcrystalline cellulose (MCC) was investigated. Three mineral doses (5, 10 and 15 mg/L) were evaluated
and the response to trace metal addition was monitored by the methane yield (YCH4) and specific methanogenic activity (SMA). A clear stimulation of the YCH4 and SMA on MCC due to the presence of minerals with a high content of trace elements was observed, respectively: the YCH4 and SMA of the sludge with 5 mg/L of high-Fe-Mg mineral increased to 397 NmLCH4/gVSsubstrate and 0.267 gCODNmLCH4/gVSinoculum/d compared to 303 NmLCH4/gVSsubstrate and 0.205 gCODNmLCH4/gVSinoculum/d in a medium without adding mineral. An increase in the doses of high-Ca mineral highly decreased methane production and process stability, due to a possible inhibition of the anaerobic digestion by calcium ions.
Anaerobic digestion (AD) reduces the amount of waste and generates products of value, such as biogas and nutrient-rich digestate. Contrary to the wide dissemination of digesters in rural areas where animal manure is used as feedstock and despite its apparent potential, AD still plays a negligible role as a treatment option for organic kitchen and market waste in cities of low-and middle-income countries.
This book compiles existing and recently generated knowledge on AD of urban biowaste at small and medium scale with special consideration given to the conditions prevailing in developing countries. Written for actors working in the waste and renewable energy sector, the book is divided into two parts: Part 1 focuses on practical information related to the AD supply chain (substrate-, process-, and product chain), and Part 2
presents selected case studies from around the world.
Trace metals are essential for the enzyme cofactors involved in the biochemistry of methane formation and are needed in a balanced anaerobic digestion process. Food and kitchen waste generally contains low concentrations of trace elements, especially metals. As a consequence the anaerobic digestion process may result instable. The aim of this study is to evaluate the effect of metals addition on mesophilic anaerobic digestion of food waste, both in batch tests and in laboratory scale CSTR reactors.
Batch anaerobic trials using source-separated food waste as substrate with inoculums of different origins were carried out under mesophilic conditions. Reactions were operated both with and without trace elements (Co, Mo, Ni, Se, W) supplementation. Supplementation with trace metals had either neutral or slightly negative effects with inoculums originating from reactors with a high background level of metals, such as those for the co-digestion of biowaste and waste activated sludge. For inoculums from reactors treating food waste only, which inherently contain low levels of trace metals, supplementation with these metals increased methane production. In particular, Mo concentrations in the range of 3-12 mg/kgTSfed and Se concentrations of 10 mg/kgTSfed increased methane production to as high as 30-40 %. Supplementation with a metal mixture (Co, Mo, Ni, Se, W) increased the methane production to the range 45-65 % for inoculums with low background concentrations of trace metals. These findings demonstrate the importance of Co, Mo, Ni, Se, W for high-performance anaerobic digestion process.
Trace metals additions that showed the best batch results (100mgNi/kgTSfed, 100mgCo/kgTSfed, 6mgMo/kgTSfed, 10mgSe/kgTSfed, 10mgW/kgTSfed) were selected for CSTR experimentation. Performances of a continuous anaerobic digester fed with trace elements were compared to a “control reactor” fed with the same substrate but without metals addition. Preliminary CSTR results showed thatmetals addition allowed for a stable anaerobic digestion process at Organic Loading Rate greater than 3 kgVSfed m3•d but were not essential.
Esse artigo apresenta uma revisão sobre os diferentes protocolos para a determinação da atividade metanogênica específica (AME) de lodos anaeróbios. Os protocolos propostos se diferem tanto em relação aos procedimentos adotados para a incubação do lodo, quanto ao método utilizado para quantificação do metano produzido durante o teste. São discutidos os princípios dos métodos manométricos e volumétricos, e descritos brevemente os protocolos de incubação do lodo, de medição do metano e o procedimento para cálculo da AME obtida pelos métodos mais utilizados pela comunidade científica nacional.
The availability of trace metals as micro-nutrients plays a very significant role on the performance and stability of agricultural biogas digesters, which are operated with energy crops, animal excreta, crop residues, organic fraction of municipal solid wastes or any other type of organic waste. The unavailability of these elements in biogas digesters is probably the first reason of poor process efficiency without any other obvious reason, despite proper management and control of other operational and environmental parameters. However, trace metal requirements of biogas digesters operated with solid biomass are not often reported in literature. Therefore, the aim of this article is to review the previous and current literature about the trace metal requirements of anaerobic biogas digesters operated with solid organic substrates for production of methane.Research highlights► The availability of trace metals plays a very significant role on the performances of agricultural biogas digesters operated with biomass. ► Poor performance efficiency without any obvious reason should be related to unavailability of trace metals. ► This article presents an overview of research studies carried out on trace metal requirements of anaerobic digesters operated with biomass. ► Use of advanced molecular biology techniques could help in understanding the trace element requirements of Archaea.
Completely mixed batch reactors were used to compare the methane production from maize at inoculum to substrate volatile solids ratios (r I/S) of 3, 2, 1.5 and 1. The tests were carried out at 35 8C and run against a control of inoculum without substrate. The stability and progress of the reaction from solid substrate to gaseous end product was monitored by measuring the pH, soluble chemical oxygen demand (CODs), total alkalinity (TA), volatile fatty acids (VFA) and gas composition on a daily basis. The results showed that the yield coefficient showed little variation over the range used, with an average value of 211 AE 6 ml CH 4 at standard temperature and pressure (STP) conditions g VS À1 added . The methane production curves were further analysed to give values for the maximum specific methane production rate, ranging from 10 ml CH 4 g VSS À1 day À1 for a r I/S of 3–23 ml CH 4 g VSS À1 day À1 for a r I/S of 1. The initial buffering capacity of the system was enhanced by addition of NaHCO 3 to 9100 mg CaCO 3 l À1 which allowed digestion to proceed within the pH range 7.2–8.0 and at TVFA to TA ratio below the critical limit of 0.4. The largest proportion of the CODs was in the form of VFA and the reactor with the highest VS loading showed an accumulation of longer chain acids.
This study sought to evaluate the efficacy of aerobic and anaerobic composting of inoculated banana peels, and assess the agronomic value of banana peel-based compost. Changes in the chemical composition under aerobic and anaerobic conditions were examined for four formulations of banana peel-based wastes over a period of 12weeks. The formulations i.e. plain banana peel (B), and a mixture with either cow dung (BC), poultry litter (BP) or earthworm (BE) were separately composted under aerobic and anaerobic conditions under laboratory conditions. Inoculation with either cow dung or poultry litter significantly facilitated mineralization in the order: BP>BC>B. The rate of decomposition was significantly faster under aerobic than in anaerobic composting conditions. The final composts contained high K (>100gkg(-1)) and TN (>2%), indicating high potential as a source of K and N fertilizer.
The objective of this study was to characterise anaerobic batch biodegradation of potato waste alone and when co-digested with sugar beet leaves. The effects of increasing concentration of potato waste expressed as percentage of total solids (TS) and the initial inoculum-to-substrate ratio (ISR) on methane yield and productivity were investigated. The ISRs studied were in the range 9.0–0.25 and increasing proportions of potato waste from 10% to 80% of TS. A maximum methane yield of 0.32 l CH4/g VSdegraded was obtained at 40% of TS and an ISR of 1.5. A methane content of up to 84% was obtained at this proportion of potato waste and ISR. Higher ISRs led to faster onset of biogas production and higher methane productivity. Furthermore, co-digestion of potato waste and sugar beet leaves in varying proportions was investigated at constant TS. Co-digestion improved the accumulated methane production and improved the methane yield by 31–62% compared with digestion of potato waste alone.
In this study, it was observed that in experimental work under laboratory scale using conventional biochemical methane potential (BMP) assay, the loading rate ratio 4:1 had optimum biodegradability rate than other ratios which were investigated, while the loading rate ratio of 1:1 had optimum biogas and methane yield after 15 days hydraulic retention time. It was concluded that chicken waste (CM) mono-digestion has higher biodegradability rate compare to organic fraction municipality solid waste (OFMSW) mono-digestion. Co-digestion of OFMSW and CM stabilizes conditions in digestion process such as carbon to nitrogen (C:N) ratio in the substrate mixtures as well as macro and micronutrients, pH, inhibitors or toxic compounds, dry matter and thus increasing biogas production. It was concluded that the organic waste generated in the municipal landfills could be co-digested with CM to produce methane which can be used as a source of environmentally friendly and clean energy for the transport sector, industries and residential homes.
The objective of this study was to assess total concentration and chemical fractionation of trace metals in the industrial wastewater and sludge collected from seven different types of industries in Dhaka City, Bangladesh. The sludge from industries is either dumped on landfills or reused as secondary resources in order to preserve natural resources. Metals were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The ranges of Cr, Ni, Cu, As, Cd, and Pb in the sludges were 1.4-9,470, 4.8-994, 12.8-444, 2.2-224, 1.9-46.0 and 1.3-87.0 mg/kg, respectively. As a whole, the average concentrations of trace metals in samples were in the decreasing order of Cr > Ni > Cu > As > Pb > Cd. The results of the Community Bureau of Reference (BCR) sequential extraction showed that the studied metals were predominantly associated with the residual fraction followed by the oxidizable fraction. The study revealed that the mobile fractions of trace metals are poorly predictable from the total content, and bioavailability of all fractions of elements tends to decrease.
The potential to recover bioenergy from anaerobic digestion of water hyacinth (WH) and from its co-digestion with fruit and vegetable waste (FVW) was investigated. Initially, biogas and methane production were studied using the biochemical methane potential (BMP) test at 2 g volatile solids (VS) L-1 of substrate concentration, both in the digestion of WH alone and in its co-digestion with FVW (WH-FVW ratio of 70:30). Subsequently, the biogas production was optimized in terms of total solids (TS) concentration, testing 4 and 6% of TS. The BMP test showed a biogas yield of 0.114 m3 biogas kg-1 VSadded for WH alone. On the other hand, the biogas potential from the WH-FVW codigestion was 0.141 m3 biogas kg-1 VSadded, showing an increase of 23% compared to that of WH alone. Maximum biogas production of 0.230 m3 biogas kg-1 VSadded was obtained at 4% of TS in the co-digestion of WH-FVW. Using semi-continuously stirred tank reactors, 1.3 m3 biogas yield kg-1 VSadded was produced using an organic loading rate of 2 kg VS m-3 d-1 and hydraulic retention time of 15 days. It was also found that a WH-FVW ratio of 80:20 improved the process in terms of pH stability. Additionally, it was found that nitrogen can be recovered in the liquid effluent with a potential for use as a liquid fertilizer.
Water purification and wastewater treatment generate sludge, which must be adequately handled to prevent detrimental effects to the environment and public health. In this study, we examined the influence of the application of settled sludge from a drinking water treatment plant (SDWTP) on the anaerobic digestion (AD) of the thickened primary sludge from a municipal wastewater treatment plant (SWWTP) which uses chemically assisted primary treatment (CAPT). On both plants the primary coagulant is ferric chloride. The study was performed at laboratory scale using specific methanogenic activity (SMA) tests, in which mixtures of SWWTP-SDWTP with the ratios 100:00, 80:20, 75:25, 70:30 and 00:100 were evaluated. Methane detection was also performed by gas chromatography for a period of 30 days. Our results show that all evaluated ratios that incorporate SDWTP, produce an inhibitory effect on the production of methane. The reduction in methane production ranged from 26% for the smallest concentration of SDWTP (20%) to more than 70% for concentrations higher than 25%. The results indicated that the hydrolytic stage was significantly affected, with the hydrolysis constant Kh also reduced by approximately 70% (0.24-0.26 day(-1) for the different ratios compared with 0.34 day(-1) for the SWWTP alone). This finding demonstrates that the best mixtures to be considered for anaerobic co-digestion must contain a fraction of SDWTP below 20%.
Stability and maturity are important criteria to guarantee the quality of a compost that is applied to agriculture or used as amendment in degraded soils. Although different techniques exist to evaluate stability and maturity, the application of laboratory tests in municipalities in developing countries can be limited due to cost and application complexities. In the composting facilities of such places, some classical low cost on-site tests to monitor the composting process are usually implemented; however, such tests do not necessarily clearly identify conditions of stability and maturity. In this article, we have applied and compared results of stability and maturity tests that can be easily employed on site (i.e. temperature, pH, moisture, electrical conductivity [EC], odor and color), and of tests that require more complex laboratory techniques (volatile solids, C/N ratio, self-heating, respirometric index, germination index [GI]). The evaluation of the above was performed in the field scale using 2 piles of biowaste applied compost. The monitoring period was from day 70 to day 190 of the process. Results showed that the low-cost tests traditionally employed to monitor the composting process on-site, such as temperature, color and moisture, do not provide consistent determinations with the more complex laboratory tests used to assess stability (e.g. respiration index, self-heating, volatile solids). In the case of maturity tests (GI, pH, EC), both the on-site tests (pH, EC) and the laboratory test (GI) provided consistent results. Although, stability was indicated for most of the samples, the maturity tests indicated that products were consistently immature. Thus, a stable product is not necessarily mature. Conclusively, the decision on the quality of the compost in the installations located in developing countries requires the simultaneous use of a combination of tests that are performed both in the laboratory and on-site.
To solve the pollution problem of extraction wastewater in citric acid production, an integrated citric acid-methane production process was proposed. Extraction wastewater was treated through anaerobic digestion and the anaerobic digestion effluent (ADE) was recycled for the next batch of citric acid fermentation, thus eliminating wastewater discharge and reducing water consumption. Excessive Na(+) contained in ADE could significantly inhibit citric acid fermentation in recycling and was removed by electrodialysis in this paper. Electrodialysis performance was improved after pretreatment of ADE with air stripping and activated carbon adsorption to remove precipitable metal ions and pigments. Moreover, the concentrate water was recycled and mixed with feed to improve the water recovery rate above 95% in electrodialysis treatment, while the dilute water was collected for citric acid fermentation. The removal rate of Na(+) in ADE was above 95% and the citric acid production was even higher than that with tap water.
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The aim of this study was to evaluate the effect of different livestock inoculums on the anaerobic digestion of food waste (FW). Five different livestock dungs i.e., poultry dung (PD), goat dung (GD), cow dung (CD), piggery dung (PGD) and rhinoceros dung (RD) were utilized as inoculums and their effects were valued in various food to microorganism (F/M) ratios in batch reactors. Different livestock dungs achieved higher methane production and volatile solids (VS) reduction in different F/M ratios such as PD, GD, CD, PGD and RD achieved at F/M ratio maintained at 1.5, 2, 2, 1.5 and 1.5, respectively. The results indicated that CD and PGD inoculum were more suitable for the anaerobic digestion of FW than other livestock dungs. Reactors inoculated with CD achieved higher methane production (227 mL g−1 VS degraded) and volatile solids degradation (54.58%) at F/M ratio maintained at 2.
Abstract Two-phase anaerobic systems are being increasingly implemented for the treatment of both sewage sludge and organic fraction of municipal solid waste. Despite the good amount of mathematical models in anaerobic digestion, few have been applied in two phase systems. In this study, a three-reaction mechanistic model has been developed, implemented and validated by using experimental data from a long-term anaerobic two-phase (TPAD) digester treating sewage sludge. A sensitivity analysis shows that the most influential parameters of the model are the ones related to the hydrolysis reaction and the activity of methanogens in the thermophilic reactor. The calibration procedure highlights a noticeable growth rate of the thermophilic methanogens throughout the evaluation period. Overall, all the measured variables are properly predicted by the model during both the calibration and the cross-validation periods. The model's representation of the organic matter behavior is quite good. The most important disagreements are observed for the biogas production especially during the validation period. The whole application procedure underlines the ability of the model to properly predict the behavior of this bioprocess.
This article provides the methane yield of municipal solid waste and its main constituents using the biochemical methane potential (BMP) test. The methane yield of kitchen waste (KW), paper waste (PW), and garden waste (GW) were 357 ( – 24.7), 147 ( – 17.1), and 114 ( – 0.6) mL CH4/g VS, respectively. The hydrolysis constant in the first order kinetic model was 0.25, 0.095, and 0.121 d- 1 for KW, PW, and GW, respectively. The effect of the inoculum to substrate (I/S) ratio in the BMP test was investigated. Methane yields of 297.4 ( – 18.6), 293.5 ( – 33.9), and 378.2 ( – 10.3) mL CH4/g VS were found at I/S ratios of 1.4, 7.2, and 12.9, respectively, whereas the hydrolysis constants were 0.112, 0.151, and 0.221 d- 1. A new method based on the production of soluble
chemical oxygen demand (SCOD) while selectively inhibiting methanogenesis has been used to determine the hydrolysis constant (0.25 d- 1) according to its true definition, which is the conversion of particulate COD to SCOD, showing that the method based on methane evolution can underestimate the actual value when hydrolysis is not the rate-limiting step.
Specific Methanogenic Activity (SMA) allowws to quantify the maximum methane producing capacity by the group of microorganisms present in anaerobic sludge. The AME, beside being used for monitoring the quality of the sludge in anaerobic reactors, is a tool that evaluates the behavior of contaminated biomass and determines the maximum organic load that can be applied to a system, in order to examine the degradability substrates and the possibility of selection of inoculants. This tool, widely used in different countries and developed more than two decades, does not have a standardized protocol that facilitates comparison of results. This article is a reflection and critical description of the methodology AME, supported by national and international experiences, with the objective of seeking uniformity in the application of the method nationwide.
The uncontrolled discharge of large amounts of food waste (FW) causes severe environmental pollution in many countries. Within different possible treatment routes, anaerobic digestion (AD) of FW into biogas, is a proven and effective solution for FW treatment and valorization. The present paper reviews the characteristics of FW, the principles of AD, the process parameters, and two approaches (pretreatment and co-digestion) for enhancing AD of food waste. Among the successive digestion reactions, hydrolysis is considered to be the rate-limiting step. To enhance the performance of AD, several physical, thermo-chemical, biological or combined pretreatments are reviewed. Moreover, a promising way for improving the performance of AD is the co-digestion of FW with other organic substrates, as confirmed by numerous studies, where a higher buffer capacity and an optimum nutrient balance enhance the biogas/methane yields of the co-digestion system.
Heavy metals affect the biochemical reactions that take place during anaerobic digestion processes of organic matter. In this review, the different effects observed in anaerobic digestion processes and during the production of biomethane and biohydrogen from several substrates contaminated with and/or inheriting heavy metals from the substrates themselves were discussed. It has been found that heavy metals exert important roles in biochemical reactions. Heavy metals like copper, nickel, zinc, cadmium, chromium and lead have been overwhelmingly reported to be inhibitory and under certain conditions toxic in biochemical reactions depending on their concentrations. Heavy metals like iron may also exhibit stimulatory effects, but these effects have been scantily observed. This review also concludes that the severity of heavy metal inhibition depends upon factors like metal concentration in a soluble, ionic form in the solution, type of metal species, and amount and distribution of biomass in the digester or chain of biochemical reactions which constitute the anaerobic digestion process. A majority of studies have demonstrated that the toxic effect of heavy metals like chromium, cadmium and nickel is attributable to a disruption of enzyme function and structure by binding of the metal ions with thiol and other groups on protein molecules or by replacing naturally occurring metals in enzyme prosthetic groups. This review has not found published data on the effects of heavy metals on the hydrolysis stage of anaerobic digestion process chemistry, and hence further studies are required to depict any changes.
The feasibility of digesting energy crops supplemented with macro- and micronutrients instead of manure, without the commonly applied long hydraulic retention time (HRT), was investigated in long-term, single-stage continuous stirred tank processes. The crops used were mixtures of sugar beets, maize and whole crop triticale. The organic loading rate (OLR) measured as a total solid (TS) was 1.5–5.5 kg m−3 d−1 and the HRT from 30 to 40 days. The results showed high methane yields, comparable to those in batch digestion, and high stability. The digestion of beets only was most stable, and showed the highest average TS-based methane yield (383 ± 26 m3 kg−1) at an OLR of 4.5 kg m−3 d−1 and a HRT of 40 days. No significant difference in methane yield was found for all the crop mixtures during stable operation. Nutrient addition therefore showed the same stimulatory and stabilising effects as manure with high methane yields achieved at relatively short HRTs.
Determination of anaerobic degradation rates and toxic effects of nitrobenzene (NB) on acetate utilizing methanogens was the first objective of this research. Serum bottles were used for anaerobic toxicity assays with an acetate enrichment culture of methanogens. Ten mg/l of nitrobenzene did not inhibit total gas production in the acetate enrichment methanogenic culture. Twenty and thirty mg/l of nitrobenzene caused reversible inhibition of methanogenesis. Batch kinetic experiments showed that 20 mg/l of nitrobenzene was degraded with a first-order rate constant, k, of 0.37 d−1. Acetate was not degraded during the first 7 days when the measured nitrobenzene concentration was higher than about 1 mg/l. The second objective was to determine the effect of zinc on nitrobenzene degradation in methanogenic systems. Ten mg/l of spiked zinc caused a reduction of gas production in the systems with 10 mg/l of nitrobenzene; 20 mg/l of zinc led to failures of systems with 10 and 20 mg/l of nitrobenzene. With 10 and 20 mg/l of added zinc, the k value for nitrobenzene degradation decreased to 0.18 d−1 and 0.14 d−1, respectively. With 20 mg/l of Zn, acetate was not degraded at all even after nitrobenzene concentration reached 0.1 mg/l, indicating toxicity of Zn to methanogenesis. Abiotic control tests with autoclaved culture showed that adsorption alone could remove 60–70% of spiked nitrobenzene in 36 days. However, the samples extracted from solids in the methanogenic test systems showed that nitrobenzene was below the detection limit of 0.1 mg/l, indicating biodegradation of nitrobenzene in these systems. Traces of benzene were seen as an intermediate in the liquid samples. Headspace analysis showed that nitrobenzene and benzene were below detection limits.
Techniques are presented for measuring the biodegradability (Biochemical Methane Potential—BMP) and toxicity (Anaerobic Toxicity Assay—ATA) of material subjected to anaerobic treatment. These relatively simple bioassays can be conducted in most research laboratories without the need for sophisticated equipment. BMP is a measure of substrate biodegradability determined by monitoring cumulative methane production from a sample which is anaerobically incubated in a chemically defined medium. The ATA measures the adverse effect of a compound on the rate of the total gas production from an easily-utilized, methanogenic substrate. These techniques are demonstrated by an analysis of the BMP and ATA of processed samples of peat.
The paper presents a new methodology for the design of Sequencing Batch Reactors. The design uses the concept of the hindered settling velocity of the sludge and the solids flux theory, helping in the definition of the settling and idle times during the cycle and of the suspended solids concentration in the settled sludge. Other design routines presented in the literature use the Sludge Volume Index (30-minute settlement in the test), and the time for sludge settling in the reactor is based purely on experience, regardless of the sludge concentration during the react phase. The hindered settling velocity and the limiting solids flux are calculated based on coefficients obtained for each one of five possible sludge settleability ranges (very good, good, fair, poor and very poor). The settling coefficients have been obtained through the combination of values presented in many references, with data from a large number of operating full-scale activated sludge plants in different countries of the world. The design routine introduced in the paper is simple, practical and conceptually justifiable, and is believed to represent a step in advancement in relation to other ones currently described in classic textbooks.
Research highlights
► Abundance of trace elements at 10 demonstration biogas plants representing different technologies and different feedstocks across Europe established. ► Results compared with recent findings in literature. ► Feedstock used influences the availability of micro nutrients in digesters. ► Abundance of trace elements is improved by a large variety in feedstock whereas feeding with manure and energy crops may lead to a depletion of micro nutrients over a long time span. ► Need for further research into the successful application of trace elements in biogas plants
A mathematical model for the development of methane production from a landfill bioreactor (LFBR) treating the organic fraction of municipal solid wastes was developed from the Gompertz equation. The model incorporates three biokinetic parameters: methane production lag phase time, rate, and potential. The methane converting capacity test experiment was conducted to monitor the specific methane production rate consuming anaerobic fermentative intermediates, including carbohydrates, proteins, and lipids. The model developed in this study can be used to predict methane production based on the chemical nature and the decomposition characteristics of the organic fraction of municipal solid wastes. The simulative results indicate that the leachate recycle for the LFBR resulted in a more rapid methane production from the consumption of the carbohydrate but in less rapid production from that of the protein and lipid. Moreover, the same specific methane production rate of 2.6 mL/g volatile solid (VS) per day occurred at the LFBR with/without leachate recycle; however, a sharp drop in methane production lag phase time, from 125 to 25 days, was obtained at the LFBR incubated with leachate recycle.
Batch experiments were performed to investigate the effect of particulate protein size on the hydrolysis of casein in anaerobic degradation. Whereas particle size did not affect the ultimate protein degradation efficiency, the hydrolysis rate coefficient increased from 0.034 to 0.298 day–1 with a change in specific surface area from 0.01 to 0.192 m2/g. The maximum rate of methane production increased from 6 to 14 mL of CH4 per gram of COD added per day with the same change in specific surface area, although the ultimate volume of methane produced was approximately the same despite the change in specific surface area. A mathematical relationship between the hydrolysis rate coefficient and the specific surface area was developed, and a new hydrolysis equation was proposed and verified.
A protocol was developed for determining the biochemical methane potential (BMP) of plant material using the OxiTop(®) system. NaOH pellets for CO(2) absorption and different pretreatment methods were tested for their influence in the BMP test. The use of NaOH pellets in the headspace of the bottle negatively affected the stability of the test increasing the pH and inhibiting methanization. Sample comminution increased the biodegradability of plant samples. Our results clearly indicate the importance of test conditions during the assessment of anaerobic biodegradability of plant material, considering BMP differences as high as 44% were found. Guidelines and recommendations are given for screening plant material suitable for anaerobic digestion using the OxiTop(®) system.
A pH-phased two-stage fermentation process combined thermophilic hydrogen production and mesophilic methane production with recirculation of the digested sludge was suggested in this study and its treatment performance was demonstrated by a continuous experiment treating organic fraction of municipal solid wastes (OFMSW). A thermophilic hydrogen production reactor was operated at a hydraulic retention time (HRT) of 1.3 days, corresponding to a loading rate of 38.4 kg-VS/m3/d or 64.4 kg-CODCr/m3/d. The short HRT and low pH applied here were enough to separate hydrogen production from methanogenesis. The mixed slurry with a high concentration of organic acids was then converted into CH4 by the mesophilic methane production reactor at a short HRT of 5.0 days, corresponding to a loading rate of 6.6 kg-VS/m3/d or 16.3 kg-CODCr/m3/d. The experiment was continued for over 150 days, and a stable performance for the simultaneous hydrogen and methane production was obtained. The yields of hydrogen and methane in this study were 205 ml H2/g VS added and 464 ml CH4/g VS added, respectively.
The objective of this study was to investigate the effects of particle size reduction and solubilization on biogas production from food waste (FW). To clarify the effects of volatile fatty acids (VFAs) in the digestion process, the relationship between particle size and VFA accumulation was investigated in detail. For this purpose, substrates of various particle sizes were prepared by bead milling to support hydrolysis. Batch anaerobic digestion experiments were carried out using these pretreated substrates at mesophilic temperature for a period of 16 days. The results of pretreatment showed that the mean particle size (MPS) of substrates ground with a bead mill decreased from 0.843 to 0.391 mm, and solubilization accounted for approximately 40% of the total chemical oxygen demand (total COD) for grinding pretreatment by bead milling. Anaerobic digestion batch experiments revealed that MPS reduced by bead milling at 1000 rpm improved methane yield by 28% compared with disposer treatment. Moreover, this may have increased microbial degradation during the VFA production process with increasing total number of revolutions (operation time × revolutions per minute). However, excessive reduction of the particle size of the substrate resulted in VFA accumulation, decreased methane production, and decreased solubilization in the anaerobic digestion process. These results suggest that optimized reduction of the particle size of the substrate in conjunction with optimized microbial growth could improve the methane yield in anaerobic digestion processes.
The characterization of solid wastes is a necessary step before they can be used in anaerobic digestion. The quantities of different compounds (carbohydrates, proteins, lipids and fibers) and anaerobic biodegradability (capacity to produce methane) are important information required to characterize waste. The Biochemical Methane Potential (BMP) test is one of the most relevant tests for assessing the biodegradability of waste materials. The BMP test is run under anaerobic conditions, using bacteria populations, which makes it very time consuming, i.e., about 30 days. This paper presents alternative methods for determining the anaerobic biodegradability of solid waste. First, we describe the already existing tests for characterizing organic matter. Then we correlate an aerobic test with an anaerobic test in order to estimate anaerobic biodegradability and biogas production. This shortens the analysis time to 5 days. Models using physico-chemical characteristics as input data (total carbohydrate, total nitrogen, fiber, etc.) can predict the amount of methane produced by correlation. Pyrolysis is a very fast analytical test that can be used to characterize solid waste. Lastly, spectroscopy techniques seem to be useful for determining biodegradability, in particular by taking into account the interaction between different molecules in the organic matter.
The paper presents the results of investigation of methane fermentation of sewage sludge and organic fraction of municipal solid wastes (OFMSW) as well as the cofermentation of both substrates under thermophilic and mesophilic conditions. In the first experiment the primary sludge and thickened excess activated sludge were fed into a 40 dm3 bioreactor operated thermophilically. The second co-fermentation experiment was conducted with the mixture of sewage sludge (75%) and OFMSW (25%) in the same bioreactor arrangement. The other three experiments (III and IV, V) were carried out in quasi-continuous mode in two separated stages: acidogenic digestion in the continuous stirred tank bioreactor under thermophilic conditions (56 °C) and mesopholic methane fermentation (36 °C). The third experiment was conducted with the substrate-OFMSW only, in the fourth run sewage sludge from a municipal water treatment plant was used. In the fifth experiment a mixture of sewage sludge and OFMSW was used. In all experiments the following data were determined: biogas content and productivity, pH, total suspended and volatile solids, elemental content (C, H, N, S) of sludge, OFMSW and inoculum, total organic carbon, total alkalinity and volatile fatty acid content. Comparing the elemental analysis of sewage sludge and OFMSW it is evident that N content is higher in the sludge than in the OFMSW, however, the carbon content relation is the opposite, which may be beneficial to methane yield of co-digestion. Methane concentration in the biogas was above 60% in all cases. Biogas productivity varied between 0.4 and 0.6 dm3/g VSSadd depending on substrate added to the digester. The obtained results are generally consistent with literature data.
Evaluation of fed-batch composing, with three different moisture conditions, for Korean food wastes was conducted using the water extractable total organic carbon content (TOCw) of mixed materials. Composting with about 50% initial moisture content was slightly more effective than composting with about 60% initial moisture content and of that where the moisture content was constantly controlled at about 50%. These different efficiencies were shown well by various indices of the composting rates, especially those based on variations of the TOCw in the mixed materials. The TOCw content represents the easily biodegradable components of organic waste, rather than the volatile or dry solids contents. The rates of the TOCw degradation showed relatively good correlations with the rates of the total wet weight reduction, as well as the rate of CO2 evolution, during the composting process. Therefore, it could also be used as a more appropriate index for the evaluation of this kind of high-rate composting process. Additionally, variations in the TOCw clearly followed the Arrhenius equation and its degradation could be estimated quantitatively using a first order reaction model. Moreover, the percentage of TOCw degradation in each cycle could be predicted based on the similarity of variations in the TOCw of each cycle in a fed-batch composting process.
A series of experiments with 0, 1, 3, 5, and 7 g Ca2+/l using calcium chloride were performed to evaluate the effect of various calcium concentrations on anaerobic digestion of swine wastewater. The addition of 3 g/l gave the best performance. On the other hand, the calcium concentrations of 5–7 g/l had an inhibitory effect on anaerobiosis. The lag phase durations expected in biogas production were 28–31 days with the addition of 0–3 g/l of calcium, and 43–52 days for calcium concentrations of 5 g/l or more. The concentrations of total volatile fatty acids decreased to less than 100 mg/l with calcium concentrations of 3–7 g/l. On the other hand, propionate and i-valerate concentrations remained over 4 and 0.8 g/l, respectively, when 1 g/l or less of calcium was added.
Biochemical methane potential tests were conducted to evaluate the effect of using a blank versus a pre-incubated inoculum in digestion of primary sludge at different waste to inoculum ratios (S/X). In addition, this study explored the influence of using two different anaerobic inoculum sources on the digestion of food waste: digested sludge from a municipal wastewater treatment plant and from a digester treating the organic fraction of municipal solid wastes. The results revealed that although there was no significant difference in methane yield (on average 114mLCH(4)/g TCOD(sub)) or biodegradability (on average 28.3%) of primary sludge using pre-incubated or non-incubated inocula, the maximum methane production rates using non-incubated inoculum were higher than those using pre-incubated inoculum at all S/X ratios. Moreover, interestingly the inoculum from an anaerobic digester treating municipal wastewater sludge was superior over the inoculum from anaerobic digester treating food waste in digesting food waste.